diff --git a/src/assets/sprites/spr_shadow_basic.png b/src/assets/sprites/spr_shadow_basic.png
new file mode 100644
index 0000000..f2b6d12
Binary files /dev/null and b/src/assets/sprites/spr_shadow_basic.png differ
diff --git a/src/presentation/states/state_ingame.c b/src/presentation/states/state_ingame.c
index 1644454..bda6dfc 100644
--- a/src/presentation/states/state_ingame.c
+++ b/src/presentation/states/state_ingame.c
@@ -47,6 +47,8 @@ static void state_enter(Presentation_State *state) {
 
     // TODO: SS - Maybe put the textures in an array and index them using an enum?
     // These should probably be loaded at start-up instead of here.
+    ctx->texture_shadow_basic = LoadTexture("assets/sprites/spr_shadow_basic.png");
+    assert(IsTextureValid(ctx->texture_shadow_basic));
     ctx->texture_grass = LoadTexture("assets/sprites/spr_floor_grass.png");
     assert(IsTextureValid(ctx->texture_grass));
     ctx->texture_apple = LoadTexture("assets/sprites/spr_food_apple.png");
@@ -60,6 +62,8 @@ static void state_enter(Presentation_State *state) {
 static void state_tick(Presentation_State *state) {
     Presentation_State_Ingame_Context *ctx = (Presentation_State_Ingame_Context *)state->context;
     (void)ctx;
+
+    game_session_tick(g_current_session);
     
     { // TEMP: SS
         if(IsKeyPressed(KEY_ESCAPE)) {
@@ -74,7 +78,8 @@ static void state_render(Presentation_State *state) {
 
     ClearBackground((Color) { 240, 236, 226, 255 });
 
-    Game_World *world = g_current_session->simulation_world.game_world;
+    Simulation_World *sim_world = &g_current_session->simulation_world;
+    Game_World *world = sim_world->game_world;
     Grid *grid = &world->grid;
 
     uint32_t grid_total_size = grid->width * grid->height;
@@ -107,74 +112,99 @@ static void state_render(Presentation_State *state) {
             uint32_t pres_y = y * GRID_CELL_SIZE;
 
             Grid_Cell *cell = &grid->cells[i];
-            Entity *entity = &cell->entity;
-            switch(entity->type) {
-                case Entity_Type_None: {
-                    break;
-                }
-                case Entity_Type_Snake_Head:
-                case Entity_Type_Snake_Body: {
-                    Color tint = (Color) { 255, 135, 102, 255 }; // TODO: SS - Get tint based on player ID.
-
-                    Vector2 origin = (Vector2) { GRID_CELL_SIZE/2, GRID_CELL_SIZE/2 };
-
-                    float sin_frequency = 0.0f;
-                    float sin_amplitude = 0.0f;
-
-                    Texture2D *texture = NULL;
-                    if(entity->type == Entity_Type_Snake_Head) {
-                        texture = &ctx->texture_snake_head;
+            if(cell->entity != NULL) {
+                Entity *entity = cell->entity;
+                switch(entity->type) {
+                    case Entity_Type_Snake_Head:
+                    case Entity_Type_Snake_Body: {
+                        Color tint = (Color) { 255, 135, 102, 255 }; // TODO: SS - Get tint based on player ID.
+    
+                        Vector2 origin = (Vector2) { GRID_CELL_SIZE/2, GRID_CELL_SIZE/2 };
+    
+                        float sin_frequency = 0.0f;
+                        float sin_amplitude = 0.0f;
+    
+                        Texture2D *texture = NULL;
+                        if(entity->type == Entity_Type_Snake_Head) {
+                            texture = &ctx->texture_snake_head;
+                        }
+                        else {
+                            texture = &ctx->texture_snake_body;
+                            // TODO: SS - If it's a body, check what index it is and use that as an y-offset to make it look cool, like a wave.
+                            sin_frequency = 4.0f;
+                            sin_amplitude = 1.0f;
+                        }
+    
+                        // Draw shadow.
+                        DrawTextureEx(
+                            ctx->texture_shadow_basic,
+                            (Vector2) { pres_x, pres_y },
+                            0.0f,
+                            1.0f,
+                            (Color) { 0, 0, 0, 32 }
+                        );
+                        
+                        DrawTexturePro(
+                            *texture,
+                            (Rectangle) { // Source.
+                                0, 0, GRID_CELL_SIZE, GRID_CELL_SIZE
+                            },
+                            (Rectangle) { // Destination.
+                                pres_x + origin.x,
+                                pres_y + origin.y + ENTITY_PRESENTATION_Y_OFFSET - (sin(GetTime() * sin_frequency)) * sin_amplitude,
+                                GRID_CELL_SIZE,
+                                GRID_CELL_SIZE
+                            },
+                            origin, // Origin.
+                            0, // Rotation.
+                            tint // Tint.
+                        );
+    
+                        break;
                     }
-                    else {
-                        texture = &ctx->texture_snake_body;
-                        // TODO: SS - If it's a body, check what index it is and use that as an y-offset to make it look cool, like a wave.
-                        sin_frequency = 4.0f;
-                        sin_amplitude = 1.0f;
+                    case Entity_Type_Food: {
+                        uint32_t flash = ((sin(GetTime() * 8) + 1)/2) * 32;
+                        Color tint = (Color) { 255-flash, 255-flash, 255-flash, 255 };
+    
+                        Vector2 origin = (Vector2) { GRID_CELL_SIZE/2, GRID_CELL_SIZE/2 };
+    
+                        // Draw shadow.
+                        DrawTextureEx(
+                            ctx->texture_shadow_basic,
+                            (Vector2) { pres_x, pres_y },
+                            0.0f,
+                            1.0f,
+                            (Color) { 0, 0, 0, 32 }
+                        );
+    
+                        DrawTexturePro(
+                            ctx->texture_apple,
+                            (Rectangle) { // Source.
+                                0, 0, GRID_CELL_SIZE, GRID_CELL_SIZE
+                            },
+                            (Rectangle) { // Destination.
+                                pres_x + origin.x,
+                                pres_y + origin.y + ENTITY_PRESENTATION_Y_OFFSET - ((sin(GetTime() * 12) + 1)/2) * 1,
+                                GRID_CELL_SIZE,
+                                GRID_CELL_SIZE
+                            },
+                            origin, // Origin.
+                            0, // Rotation.
+                            tint // Tint.
+                        );
+                        break;
                     }
-                    
-                    DrawTexturePro(
-                        *texture,
-                        (Rectangle) { // Source.
-                            0, 0, GRID_CELL_SIZE, GRID_CELL_SIZE
-                        },
-                        (Rectangle) { // Destination.
-                            pres_x + origin.x,
-                            pres_y + origin.y + ENTITY_PRESENTATION_Y_OFFSET - (sin(GetTime() * sin_frequency)) * sin_amplitude,
-                            GRID_CELL_SIZE,
-                            GRID_CELL_SIZE
-                        },
-                        origin, // Origin.
-                        0, // Rotation.
-                        tint // Tint.
-                    );
-
-                    break;
-                }
-                case Entity_Type_Food: {
-                    uint32_t flash = ((sin(GetTime() * 8) + 1)/2) * 32;
-                    Color tint = (Color) { 255-flash, 255-flash, 255-flash, 255 };
-
-                    Vector2 origin = (Vector2) { GRID_CELL_SIZE/2, GRID_CELL_SIZE/2 };
-
-                    DrawTexturePro(
-                        ctx->texture_apple,
-                        (Rectangle) { // Source.
-                            0, 0, GRID_CELL_SIZE, GRID_CELL_SIZE
-                        },
-                        (Rectangle) { // Destination.
-                            pres_x + origin.x,
-                            pres_y + origin.y + ENTITY_PRESENTATION_Y_OFFSET - ((sin(GetTime() * 12) + 1)/2) * 1,
-                            GRID_CELL_SIZE,
-                            GRID_CELL_SIZE
-                        },
-                        origin, // Origin.
-                        0, // Rotation.
-                        tint // Tint.
-                    );
-                    break;
                 }
             }
         }
+
+        { // TEMP: SS - Render match state.
+            char buf[512];
+            snprintf(&buf[0], sizeof(buf), "Match-state: %i. Tick: %lu.", sim_world->match_state, sim_world->tick);
+
+            DrawText(buf, 32, 32, 12, RED);
+        }
+
     }
     EndMode2D();
 }
@@ -184,6 +214,7 @@ static void state_exit(Presentation_State *state) {
     (void)ctx;
     printf("Exiting ingame\n");
 
+    UnloadTexture(ctx->texture_shadow_basic);
     UnloadTexture(ctx->texture_grass);
     UnloadTexture(ctx->texture_apple);
     UnloadTexture(ctx->texture_snake_head);
diff --git a/src/presentation/states/state_ingame.h b/src/presentation/states/state_ingame.h
index c002898..fdd17b5 100644
--- a/src/presentation/states/state_ingame.h
+++ b/src/presentation/states/state_ingame.h
@@ -10,6 +10,7 @@ typedef struct {
     Camera2D main_camera;
 
     // Textures.
+    Texture2D texture_shadow_basic;
     Texture2D texture_grass;
     Texture2D texture_apple;
     Texture2D texture_snake_head;
diff --git a/src/session/game_session.c b/src/session/game_session.c
index 44c360b..e480d20 100644
--- a/src/session/game_session.c
+++ b/src/session/game_session.c
@@ -4,6 +4,9 @@
 #include <stdlib.h>
 #include <assert.h>
 #include <stdio.h>
+#include <string.h>
+
+#include "raylib.h"
 
 Game_Session *g_current_session = NULL;
 
@@ -22,25 +25,127 @@ void game_session_create(bool is_singleplayer, bool is_host, Game_Session_Settin
         session->settings.level_height
     );
 
+    session->players        = (Game_Session_Player *)calloc(session->settings.max_players, sizeof(Game_Session_Player));
+    session->players_prev   = (Game_Session_Player *)calloc(session->settings.max_players, sizeof(Game_Session_Player));
+
+    { // TEMP
+        session->local_player_index = 0;
+        assert(game_session_create_player(session, &session->local_player_index));
+    }
+
     g_current_session = session;
 
     printf("New Game_Session created.\n");
 }
 
 void game_session_destroy() {
-    if(g_current_session == NULL) {
+    Game_Session *session = g_current_session;
+
+    if(session == NULL) {
         return;
     }
 
-    simulation_destroy_world(&g_current_session->simulation_world);
+    simulation_destroy_world(&session->simulation_world);
 
-    free(g_current_session);
+    free(session->players);
+    session->players = NULL;
+    free(session->players_prev);
+    session->players_prev = NULL;
+
+    free(session);
     g_current_session = NULL;
 }
 
 void game_session_init_default_settings(bool is_singleplayer, Game_Session_Settings *out_settings) {
     out_settings->seed         = 1337; // TODO: SS - Randomize.
-    out_settings->level_width  = 48;
-    out_settings->level_height = 48;
+    out_settings->level_width  = 32;
+    out_settings->level_height = 32;
     out_settings->max_players  = is_singleplayer ? 1 : 8;
+}
+
+void game_session_tick(Game_Session *session) {
+    Game_Session_Player *local_session_player = game_session_get_local_player(session);
+    assert(local_session_player != NULL);
+    local_session_player->input = (Simulation_Game_Input) { // TODO: SS - Move this somewhere else, maybe.
+        .up     = IsKeyDown(KEY_UP)     || IsKeyDown(KEY_W),
+        .down   = IsKeyDown(KEY_DOWN)   || IsKeyDown(KEY_S),
+        .right  = IsKeyDown(KEY_RIGHT)  || IsKeyDown(KEY_D),
+        .left   = IsKeyDown(KEY_LEFT)   || IsKeyDown(KEY_A)
+    };
+
+    { // TODO: SS - Use delta-time to accumulate time. Tick the simulation in a constant tick-rate.
+        // Update input.
+        for(uint16_t i = 0; i < session->settings.max_players; i++) {
+            Game_Session_Player *session_player_prev    = &session->players_prev[i];
+            Game_Session_Player *session_player         = &session->players[i];
+
+            bool was_active = session_player_prev->active;
+            bool is_active  = session_player->active;
+
+            if (!was_active && is_active) {
+                simulation_world_enqueue_command(&session->simulation_world, (Simulation_Command) {
+                    .type = Simulation_Command_Type_Add_Player,
+                    .player_id = i
+                });
+            } else if (was_active && !is_active) {
+                simulation_world_enqueue_command(&session->simulation_world, (Simulation_Command) {
+                    .type = Simulation_Command_Type_Remove_Player,
+                    .player_id = i
+                });
+            }
+
+            if(!session_player->active) {
+                continue;
+            }
+
+            simulation_world_enqueue_command(&session->simulation_world, (Simulation_Command) {
+                .type = Simulation_Command_Type_Set_Player_Input,
+                .player_id = i,
+                .player_input = session_player->input,
+            });
+        }
+        
+        // Tick.
+        simulation_world_tick(&session->simulation_world);
+
+        // Copy 'players' from session to 'players_prev'.
+        memcpy(session->players_prev, session->players, sizeof(Game_Session_Player) * session->settings.max_players);
+    }
+}
+
+Game_Session_Player *game_session_get_local_player(Game_Session *session) {
+    assert(session != NULL);
+    return &session->players[session->local_player_index];
+}
+
+bool game_session_create_player(Game_Session *session, uint16_t *out_player_index) {
+    assert(session != NULL);
+
+    int32_t found_index = -1;
+    for(uint16_t i = 0; i < session->settings.max_players; i++) {
+        Game_Session_Player *session_player = &session->players[i];
+        assert(session_player != NULL);
+        if(!session_player->active) {
+            session_player->active = true;
+            found_index = i;
+        }
+    }
+
+    if(found_index < 0) {
+        return false;
+    }
+
+    *out_player_index = (uint16_t)found_index;
+    return true;
+}
+
+void game_session_destroy_player(Game_Session *session, uint16_t player_index) {
+    assert(session != NULL);
+    assert(player_index < session->settings.max_players);
+    
+    Game_Session_Player *player = &session->players[player_index];
+    assert(player != NULL);
+    assert(player->active);
+
+    memset(player, 0, sizeof(Game_Session_Player));
 }
\ No newline at end of file
diff --git a/src/session/game_session.h b/src/session/game_session.h
index d7a0a74..ca003cd 100644
--- a/src/session/game_session.h
+++ b/src/session/game_session.h
@@ -5,6 +5,14 @@
 #include <stdbool.h>
 
 #include "simulation/simulation_world.h"
+#include "simulation/input.h"
+#include "simulation/player.h"
+
+typedef struct {
+    bool active;
+
+    Simulation_Game_Input input;
+} Game_Session_Player;
 
 typedef struct {
     uint32_t seed;
@@ -23,9 +31,13 @@ typedef struct {
 
     Game_Session_Settings settings;
 
-    // TODO: SS - Game-state (counting down, active, over)
-    // TODO: SS - Local(?) input-queue.
     Simulation_World simulation_world;
+
+    Game_Session_Player *players;
+    Game_Session_Player *players_prev;
+    uint16_t local_player_index;
+
+    // TODO: SS - Local + remote input-queue.
 } Game_Session;
 
 extern Game_Session *g_current_session;
@@ -35,4 +47,11 @@ void game_session_destroy();
 
 void game_session_init_default_settings(bool is_singleplayer, Game_Session_Settings *out_settings);
 
+void game_session_tick(Game_Session *session);
+
+Game_Session_Player *game_session_get_local_player(Game_Session *session);
+
+bool game_session_create_player(Game_Session *session, uint16_t *out_player_index);
+void game_session_destroy_player(Game_Session *session, uint16_t player_index);
+
 #endif
\ No newline at end of file
diff --git a/src/shared/entity.h b/src/shared/entity.h
index 9c5bf3a..41bcfaa 100644
--- a/src/shared/entity.h
+++ b/src/shared/entity.h
@@ -3,8 +3,11 @@
 
 #include <stdint.h>
 
+typedef uint16_t Entity_ID;
+
+#define INVALID_ENTITY_ID Entity_ID(65535)
+
 typedef enum {
-    Entity_Type_None,
     Entity_Type_Snake_Head,
     Entity_Type_Snake_Body,
     Entity_Type_Food,
@@ -12,6 +15,11 @@ typedef enum {
 
 typedef struct {
     Entity_Type type;
+    
+    uint16_t x;
+    uint16_t y;
+    
+    // TODO: SS - Color/tint?
 } Entity;
 
 #endif
\ No newline at end of file
diff --git a/src/shared/game_world.c b/src/shared/game_world.c
index 0fd558d..ec7448f 100644
--- a/src/shared/game_world.c
+++ b/src/shared/game_world.c
@@ -2,6 +2,7 @@
 
 #include <stdlib.h>
 #include <assert.h>
+#include <stdio.h>
 
 #define MIN_LEVEL_WIDTH 8 // TODO: SS - Move these out of here.
 #define MIN_LEVEL_HEIGHT 8
@@ -17,39 +18,55 @@ Game_World *game_world_create(uint32_t seed, uint16_t level_width, uint16_t leve
     w->max_entities = level_width * level_height;
     w->entities = (Entity *)calloc(w->max_entities, sizeof(Entity));
 
+    // Set up entity-id queue.
+    assert(squeue_init(&w->entity_id_queue, w->max_entities, sizeof(Entity_ID)));
+    for(uint16_t i = 0; i < w->entity_id_queue.capacity; i++) {
+        Entity_ID id = (Entity_ID)i;
+        assert(squeue_push(&w->entity_id_queue, &id));
+    }
+
     grid_initialize(&w->grid, level_width, level_height);
 
-    
-    { // TODO: SS - Create the level.
-        {
-            Grid_Cell *cell = grid_get_cell(&w->grid, 5, 3);
-            assert(cell != NULL);
-            cell->entity.type = Entity_Type_Food;
-        }
-
-        {
-            Grid_Cell *cell = grid_get_cell(&w->grid, 11, 4);
-            assert(cell != NULL);
-            cell->entity.type = Entity_Type_Food;
-        }
-
-        {
-            Grid_Cell *cell = grid_get_cell(&w->grid, 15, 9);
-            assert(cell != NULL);
-            cell->entity.type = Entity_Type_Food;
-        }
-
-        {
-            Grid_Cell *cell = grid_get_cell(&w->grid, 24, 15);
-            assert(cell != NULL);
-            cell->entity.type = Entity_Type_Snake_Head;
-        }
-        {
-            Grid_Cell *cell = grid_get_cell(&w->grid, 23, 15);
-            assert(cell != NULL);
-            cell->entity.type = Entity_Type_Snake_Body;
-        }
+    { // TEMP: SS - Testing ..
+        Entity_ID entity_food;
+        assert(game_world_create_entity(
+            w,
+            Entity_Type_Food,
+            4, 8,
+            &entity_food
+        ));
     }
+    
+    // { // TODO: SS - Create the level.
+    //     {
+    //         Grid_Cell *cell = grid_get_cell(&w->grid, 5, 3);
+    //         assert(cell != NULL);
+    //         cell->entity.type = Entity_Type_Food;
+    //     }
+
+    //     {
+    //         Grid_Cell *cell = grid_get_cell(&w->grid, 11, 4);
+    //         assert(cell != NULL);
+    //         cell->entity.type = Entity_Type_Food;
+    //     }
+
+    //     {
+    //         Grid_Cell *cell = grid_get_cell(&w->grid, 15, 9);
+    //         assert(cell != NULL);
+    //         cell->entity.type = Entity_Type_Food;
+    //     }
+
+    //     {
+    //         Grid_Cell *cell = grid_get_cell(&w->grid, 24, 15);
+    //         assert(cell != NULL);
+    //         cell->entity.type = Entity_Type_Snake_Head;
+    //     }
+    //     {
+    //         Grid_Cell *cell = grid_get_cell(&w->grid, 23, 15);
+    //         assert(cell != NULL);
+    //         cell->entity.type = Entity_Type_Snake_Body;
+    //     }
+    // }
 
 
     return w;
@@ -62,5 +79,65 @@ void game_world_destroy(Game_World *world) {
     world->max_entities = 0;
     free(world->entities);
     grid_dispose(&world->grid);
+    squeue_free(&world->entity_id_queue);
+    
     free(world);
+}
+
+bool game_world_create_entity(Game_World *world, Entity_Type type, uint16_t x, uint16_t y, Entity_ID *out_entity_id) {
+    assert(world != NULL);
+
+    if(x >= world->grid.width) {
+        printf("Failed to create entity; Invalid x-coordinate.\n");
+        return false;
+    }
+    if(y >= world->grid.height) {
+        printf("Failed to create entity; Invalid y-coordinate.\n");
+        return false;
+    }
+    
+
+    Entity_ID id = 0;
+    bool got_id = squeue_pop(&world->entity_id_queue, (void *)&id);
+    if(!got_id) {
+        printf("No free entity ids.\n");
+        return false;
+    }
+    
+    world->entities[id] = (Entity) {
+        .type = type,
+    };
+
+    Grid_Cell *cell = grid_get_cell(&world->grid, x, y); // TEMP: SS - Hardcoded coordinates. // TODO: SS - Find good coordinate.
+    assert(cell != NULL);
+    assert(grid_try_add_entity_to_cell(cell, &world->entities[id]));
+
+    *out_entity_id = id;
+    return true;
+}
+
+void game_world_destroy_entity(Game_World *world, Entity_ID entity_id) {
+    assert(world != NULL);
+
+    Entity *entity = game_world_try_get_entity_by_id(
+        world,
+        entity_id
+    );
+    assert(entity != NULL);
+
+    Grid_Cell *cell = grid_get_cell(&world->grid, entity->x, entity->y);
+    assert(cell != NULL);
+    assert(grid_try_remove_entity_from_cell(cell));
+
+    squeue_push(&world->entity_id_queue, entity_id);
+}
+
+Entity *game_world_try_get_entity_by_id(Game_World *world, Entity_ID id) {
+    assert(world != NULL);
+
+    if(id >= world->max_entities) {
+        return NULL;
+    }
+
+    return &world->entities[id];
 }
\ No newline at end of file
diff --git a/src/shared/game_world.h b/src/shared/game_world.h
index 4338e4e..e5f09ad 100644
--- a/src/shared/game_world.h
+++ b/src/shared/game_world.h
@@ -4,17 +4,25 @@
 #include <stdint.h>
 #include "entity.h"
 #include "grid.h"
+#include "shared/squeue.h"
 
 typedef struct {
     uint32_t seed;
     
+    SQueue entity_id_queue;
     Entity *entities;
     uint16_t max_entities;
 
     Grid grid;
+
 } Game_World;
 
 Game_World *game_world_create(uint32_t seed, uint16_t level_width, uint16_t level_height);
 void game_world_destroy(Game_World *world);
 
+bool game_world_create_entity(Game_World *world, Entity_Type type, uint16_t x, uint16_t y, Entity_ID *out_entity_id);
+void game_world_destroy_entity(Game_World *world, Entity_ID entity_id);
+
+Entity *game_world_try_get_entity_by_id(Game_World *world, Entity_ID id);
+
 #endif
\ No newline at end of file
diff --git a/src/shared/grid.c b/src/shared/grid.c
index b8431ae..7eab07c 100644
--- a/src/shared/grid.c
+++ b/src/shared/grid.c
@@ -6,6 +6,19 @@
 #define GRID_MIN_WIDTH 8
 #define GRID_MIN_HEIGHT 8
 
+static bool from_grid_index(Grid *grid, uint16_t grid_index, uint16_t *out_x, uint16_t *out_y) {
+    assert(grid != NULL);
+    assert(out_x != NULL);
+    assert(out_y != NULL);
+
+    if (!grid || !out_x || !out_y) return false;
+    if (grid_index >= grid->width * grid->height) return false;
+
+    *out_x = grid_index % grid->width;
+    *out_y = grid_index / grid->width;
+    return true;
+}
+
 bool grid_initialize(Grid *grid, uint16_t width, uint16_t height) {
     assert(grid != NULL);
 
@@ -16,6 +29,12 @@ bool grid_initialize(Grid *grid, uint16_t width, uint16_t height) {
     grid->width = width;
     grid->height = height;
     grid->cells = calloc(width * height, sizeof(Grid_Cell));
+
+    for(uint16_t i = 0; i < (width * height); i++) {
+        Grid_Cell *cell = &grid->cells[i];
+        assert(from_grid_index(grid, i, &cell->x, &cell->y));
+    }
+    
     return true;
 }
 
@@ -37,19 +56,6 @@ static bool to_grid_index(Grid *grid, uint16_t x, uint16_t y, uint16_t *out_grid
     return true;
 }
 
-static bool from_grid_index(Grid *grid, uint16_t grid_index, uint16_t *out_x, uint16_t *out_y) {
-    assert(grid != NULL);
-    assert(out_x != NULL);
-    assert(out_y != NULL);
-
-    if (!grid || !out_x || !out_y) return false;
-    if (grid_index >= grid->width * grid->height) return false;
-
-    *out_x = grid_index % grid->width;
-    *out_y = grid_index / grid->width;
-    return true;
-}
-
 Grid_Cell *grid_get_cell(Grid *grid, uint16_t x, uint16_t y) {
     assert(grid != NULL);
     if(x >= grid->width || y >= grid->height) return NULL;
@@ -60,4 +66,36 @@ Grid_Cell *grid_get_cell(Grid *grid, uint16_t x, uint16_t y) {
     }
     
     return &grid->cells[grid_index];
+}
+
+bool grid_try_add_entity_to_cell(Grid_Cell *cell, Entity *entity) {
+    assert(cell != NULL);
+    assert(entity != NULL);
+
+    // TODO: SS - Could check what type of cell it is to determine if
+    // we're allowed to place an entity here. Is it a wall? Lava?
+    
+    if(cell->entity != NULL) {
+        return false;
+    }
+
+    cell->entity = entity;
+    entity->x = cell->x;
+    entity->y = cell->y;
+    
+    return true;
+}
+
+bool grid_try_remove_entity_from_cell(Grid_Cell *cell) {
+    assert(cell != NULL);
+
+    if(cell->entity == NULL) {
+        return false;
+    }
+
+    cell->entity->x = 0;
+    cell->entity->y = 0;
+    cell->entity = NULL;
+
+    return true;
 }
\ No newline at end of file
diff --git a/src/shared/grid.h b/src/shared/grid.h
index ba2adb7..3325d83 100644
--- a/src/shared/grid.h
+++ b/src/shared/grid.h
@@ -7,7 +7,10 @@
 #include "entity.h"
 
 typedef struct {
-    Entity entity;
+    Entity *entity;
+
+    uint16_t x;
+    uint16_t y;
 } Grid_Cell;
 
 typedef struct {
@@ -22,4 +25,7 @@ void grid_dispose(Grid *grid);
 
 Grid_Cell *grid_get_cell(Grid *grid, uint16_t x, uint16_t y);
 
+bool grid_try_add_entity_to_cell(Grid_Cell *cell, Entity *entity);
+bool grid_try_remove_entity_from_cell(Grid_Cell *cell);
+
 #endif
\ No newline at end of file
diff --git a/src/shared/squeue.c b/src/shared/squeue.c
new file mode 100644
index 0000000..21db128
--- /dev/null
+++ b/src/shared/squeue.c
@@ -0,0 +1,57 @@
+#include "squeue.h"
+
+bool squeue_init(SQueue *q, uint16_t capacity, size_t element_size) {
+    q->buffer = malloc(element_size * capacity);
+    if (!q->buffer) {
+        return false;
+    }
+
+    q->head = q->tail = q->count = 0;
+    q->capacity = capacity;
+    q->element_size = element_size;
+
+    return true;
+}
+
+void squeue_free(SQueue *q) {
+    free(q->buffer);
+    q->buffer = NULL;
+    q->head = q->tail = q->count = q->capacity = 0;
+    q->element_size = 0;
+}
+
+bool squeue_push(SQueue *q, const void *elem) {
+    if (q->count == q->capacity) {
+        return false;
+    }
+
+    void *dest = (uint8_t*)q->buffer + q->tail * q->element_size;
+    memcpy(dest, elem, q->element_size);
+    q->tail = (q->tail + 1) % q->capacity;
+    q->count++;
+
+    return true;
+}
+
+bool squeue_pop(SQueue *q, void *out) {
+    if (q->count == 0) {
+        return false;
+    }
+
+    void *src = (uint8_t*)q->buffer + q->head * q->element_size;
+    memcpy(out, src, q->element_size);
+    q->head = (q->head + 1) % q->capacity;
+    q->count--;
+    
+    return true;
+}
+
+bool squeue_peek(const SQueue *q, void *out) {
+    if (q->count == 0) {
+        return false;
+    }
+
+    void *src = (uint8_t*)q->buffer + q->head * q->element_size;
+    memcpy(out, src, q->element_size);
+    return true;
+}
\ No newline at end of file
diff --git a/src/shared/squeue.h b/src/shared/squeue.h
new file mode 100644
index 0000000..1d5213a
--- /dev/null
+++ b/src/shared/squeue.h
@@ -0,0 +1,25 @@
+#ifndef QUEUE_H
+#define QUEUE_H
+
+#include <stdint.h>
+#include <stdlib.h>
+#include <stdbool.h>
+#include <string.h>
+
+typedef struct {
+    void *buffer;
+    uint16_t head;
+    uint16_t tail;
+    uint16_t count;
+    uint16_t capacity;
+    size_t element_size;
+} SQueue;
+
+bool squeue_init(SQueue *q, uint16_t capacity, size_t element_size);
+void squeue_free(SQueue *q);
+
+bool squeue_push(SQueue *q, const void *elem);
+bool squeue_pop(SQueue *q, void *out);
+bool squeue_peek(const SQueue *q, void *out);
+
+#endif
\ No newline at end of file
diff --git a/src/simulation/command.h b/src/simulation/command.h
new file mode 100644
index 0000000..3b34bbe
--- /dev/null
+++ b/src/simulation/command.h
@@ -0,0 +1,19 @@
+#ifndef SIM_COMMAND_H
+#define SIM_COMMAND_H
+
+#include "input.h"
+
+typedef enum {
+    Simulation_Command_Type_Add_Player,
+    Simulation_Command_Type_Remove_Player,
+    Simulation_Command_Type_Set_Player_Input,
+} Simulation_Command_Type;
+
+typedef struct {
+    Simulation_Command_Type type;
+
+    uint16_t player_id;
+    Simulation_Game_Input player_input;
+} Simulation_Command;
+
+#endif
\ No newline at end of file
diff --git a/src/simulation/input.h b/src/simulation/input.h
new file mode 100644
index 0000000..9157f34
--- /dev/null
+++ b/src/simulation/input.h
@@ -0,0 +1,12 @@
+#ifndef SIM_GAME_INPUT_H
+#define SIM_GAME_INPUT_H
+
+typedef struct {
+    // Movement can probably just be one byte. For a traditional snake-game, only one directional-input is OK.
+    bool up;
+    bool down;
+    bool right;
+    bool left;
+} Simulation_Game_Input;
+
+#endif
\ No newline at end of file
diff --git a/src/simulation/player.h b/src/simulation/player.h
new file mode 100644
index 0000000..4c13bb6
--- /dev/null
+++ b/src/simulation/player.h
@@ -0,0 +1,15 @@
+#ifndef SIM_PLAYER_H
+#define SIM_PLAYER_H
+
+#include "simulation/input.h"
+
+typedef struct {
+    bool active;
+    
+    Entity_ID entity_id;
+    Simulation_Game_Input input;
+    // score, name etc.
+
+} Simulation_Player;
+
+#endif
\ No newline at end of file
diff --git a/src/simulation/simulation_world.c b/src/simulation/simulation_world.c
index d55321b..53c9540 100644
--- a/src/simulation/simulation_world.c
+++ b/src/simulation/simulation_world.c
@@ -1,14 +1,28 @@
 #include "simulation_world.h"
 
 #include <string.h>
+#include <stdio.h>
 #include <assert.h>
 
+#define SIM_COMMANDS_PER_PLAYER 4
+
 Simulation_World simulation_create_world(uint32_t seed, uint8_t max_players, uint16_t width, uint16_t height) {
     Simulation_World w;
     memset(&w, 0, sizeof(Simulation_World));
 
-    w.game_world = game_world_create(seed, width, height);
+    w.tick = 0;
+    
+    w.game_world    = game_world_create(seed, width, height);
     assert(w.game_world != NULL);
+    
+    w.match_state   = Simulation_Match_State_Waiting_To_Start;
+    
+    w.players       = (Simulation_Player *)calloc(max_players, sizeof(Simulation_Player));
+    w.max_players   = max_players;
+    
+    w.max_commands  = w.max_players * SIM_COMMANDS_PER_PLAYER;
+    w.command_count = 0;
+    w.commands      = (Simulation_Command *)calloc(w.max_commands, sizeof(Simulation_Command));
 
     return w;
 }
@@ -18,4 +32,96 @@ void simulation_destroy_world(Simulation_World *simulation_world) {
     
     game_world_destroy(simulation_world->game_world);
     simulation_world->game_world = NULL;
+    
+    simulation_world->match_state = Simulation_Match_State_Waiting_To_Start;
+    
+    free(simulation_world->players);
+    simulation_world->players = NULL;
+    
+    free(simulation_world->commands);
+    simulation_world->commands = NULL;
+}
+
+void simulation_world_tick(Simulation_World *simulation_world) {
+    assert(simulation_world != NULL);
+
+    printf("TICK: %lu.\n", simulation_world->tick);
+    
+    for(uint16_t i = 0; i < simulation_world->command_count; i++) {
+        Simulation_Command *cmd = &simulation_world->commands[i];
+        printf("Command type: %i, player id: %i.\n", cmd->type, cmd->player_id);
+
+        Simulation_Player *player = &simulation_world->players[cmd->player_id];
+        assert(player != NULL);
+
+        switch(cmd->type) {
+            case Simulation_Command_Type_Add_Player: {
+                printf("Simulation_Command_Type_Add_Player\n");
+                assert(!player->active);
+                player->active = true;
+
+                // TODO: SS - Create entity.
+                assert(game_world_create_entity(
+                    simulation_world->game_world,
+                    Entity_Type_Snake_Head,
+                    10, 15,
+                    &player->entity_id
+                ));
+
+                break;
+            }
+            case Simulation_Command_Type_Remove_Player: {
+                printf("Simulation_Command_Type_Remove_Player\n");
+                assert(player->active);
+                player->active = false;
+
+                game_world_destroy_entity(simulation_world->game_world, player->entity_id);
+                
+                break;
+            }
+            case Simulation_Command_Type_Set_Player_Input: {
+                printf("Simulation_Command_Type_Set_Player_Input\n");
+                assert(player->active);
+                player->input = cmd->player_input;
+                
+                break;
+            }
+        }
+    }
+    simulation_world->command_count = 0;
+    
+    // Loop over all players in the simulation.
+    for(uint16_t i = 0; i < simulation_world->max_players; i++) {
+        Simulation_Player *player = &simulation_world->players[i];
+        if(!player->active) {
+            continue;
+        }
+
+        printf("* Input for player %i - up: %i, down: %i, right: %i, left: %i.\n",
+            i,
+            player->input.up, player->input.down, player->input.right, player->input.left
+        );
+
+        Entity *player_entity = game_world_try_get_entity_by_id(simulation_world->game_world, player->entity_id);
+        assert(player_entity != NULL);
+
+        printf("Entity %i ~ x: %u, y: %u.\n", player->entity_id, player_entity->x, player_entity->y);
+    }
+    
+    // TODO: SS - Game-logic! :)
+
+    simulation_world->tick += 1;
+}
+
+bool simulation_world_enqueue_command(Simulation_World *simulation_world, Simulation_Command command) {
+    assert(simulation_world != NULL);
+
+    if(simulation_world->command_count >= simulation_world->max_commands) {
+        return false;
+    }
+    
+    simulation_world->commands[simulation_world->command_count] = command;
+    simulation_world->command_count += 1;
+    
+    return true;
 }
\ No newline at end of file
diff --git a/src/simulation/simulation_world.h b/src/simulation/simulation_world.h
index 8c9202e..c308aec 100644
--- a/src/simulation/simulation_world.h
+++ b/src/simulation/simulation_world.h
@@ -4,12 +4,36 @@
 #include <stdlib.h>
 
 #include "shared/game_world.h"
+#include "player.h"
+#include "command.h"
+
+typedef enum {
+    Simulation_Match_State_Waiting_To_Start,
+    Simulation_Match_State_Counting_Down,
+    Simulation_Match_State_Active,
+    Simulation_Match_State_Ended,
+} Simulation_Match_State;
 
 typedef struct {
+    uint64_t tick;
+
     Game_World *game_world;
+
+    Simulation_Match_State match_state;
+
+    Simulation_Player *players;
+    uint16_t max_players;
+
+    Simulation_Command *commands;
+    uint16_t command_count;
+    uint16_t max_commands;
 } Simulation_World;
 
 Simulation_World simulation_create_world(uint32_t seed, uint8_t max_players, uint16_t width, uint16_t height);
 void simulation_destroy_world(Simulation_World *simulation_world);
 
+void simulation_world_tick(Simulation_World *simulation_world);
+
+bool simulation_world_enqueue_command(Simulation_World *simulation_world, Simulation_Command command);
+
 #endif
\ No newline at end of file