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-# Entity Management
-
-Entities are game objects that implement behavior and live on Grids. While Grids handle rendering and mediate interactions, Entities encapsulate game logic like movement, combat, and AI.
-
-## Quick Reference
-
-**Parent System:** [[Grid-System]]
-
-**Key Types:**
-- `mcrfpy.Entity` - Game entities on grids
-- `mcrfpy.Grid` - Spatial container for entities
-- `mcrfpy.EntityCollection` - Collection of entities on a grid
-
-**Key Files:**
-- `src/UIEntity.h` / `src/UIEntity.cpp`
-- `src/UIEntityCollection.h` / `.cpp`
-- `src/SpatialHash.h` / `src/SpatialHash.cpp` - Spatial indexing
-
-**Related Issues:**
-- [#115](../issues/115) - SpatialHash for fast queries ✅ Implemented
-- [#117](../issues/117) - Memory Pool for entities (Deferred)
-- [#159](../issues/159) - EntityCollection iterator optimization ✅ Fixed
-
----
-
-## What Are Entities?
-
-Entities are game objects that:
-- **Live on a Grid** (0 or 1 grid at a time)
-- **Have a sprite** for visual rendering
-- **Have grid position** (integer cell coordinates)
-- **Implement behavior** (movement, AI, combat, inventory)
-- **Track visibility** (which cells they can see / have seen)
-
-**Key distinction:** Entities implement behavior. Grids mediate interaction between entities and render them to screen.
-
----
-
-## Entity-Grid Relationship
-
-The Entity-Grid relationship mirrors the UIDrawable parent-child pattern:
-
-| Relationship | Property | Automatic Behavior |
-|--------------|----------|-------------------|
-| Entity → Grid | `entity.grid` | Set when added to `grid.entities` |
-| Grid → Entities | `grid.entities` | Collection of all entities on grid |
-
-```python
-import mcrfpy
-
-# Create grid and entity
-grid = mcrfpy.Grid(grid_size=(50, 50), pos=(0, 0), size=(400, 400))
-player = mcrfpy.Entity(pos=(10, 10), sprite_index=0)
-
-# Before adding: entity has no grid
-print(player.grid)  # None
-
-# Add to grid
-grid.entities.append(player)
-
-# After adding: bidirectional link established
-print(player.grid == grid)  # True
-print(player in grid.entities)  # True
-
-# Removing breaks the link
-grid.entities.remove(player)
-print(player.grid)  # None
-```
-
-**Important:** An entity can only be on 0 or 1 grids at a time. Adding to a new grid automatically removes from the old one.
-
----
-
-## Entity Properties
-
-### Position
-
-```python
-# Grid coordinates (integer cells)
-entity.x = 15
-entity.y = 20
-entity.pos = (15, 20)  # Tuple form
-
-# Draw position (float, for animation interpolation)
-print(entity.draw_pos)  # Actual render position
-```
-
-### Sprite
-
-```python
-entity.sprite_index = 5  # Index in texture sprite sheet
-```
-
-### Visibility
-
-```python
-entity.visible = True
-entity.opacity = 0.8  # 0.0 to 1.0
-```
-
-### Grid Reference
-
-```python
-current_grid = entity.grid  # Read-only, set by collection operations
-```
-
----
-
-## Spatial Queries with SpatialHash
-
-As of commit 7d57ce2, grids use **SpatialHash** for efficient spatial queries. This provides O(k) query time where k is the number of nearby entities, instead of O(n) scanning all entities.
-
-### entities_in_radius()
-
-```python
-# Query entities within a radius (uses SpatialHash internally)
-nearby = grid.entities_in_radius(x, y, radius)
-
-# Example: Find all entities within 10 cells of position (50, 50)
-threats = grid.entities_in_radius(50, 50, 10)
-for entity in threats:
-    print(f"Entity at ({entity.x}, {entity.y})")
-```
-
-### Performance Comparison
-
-| Entity Count | O(n) Query | SpatialHash | Speedup |
-|--------------|------------|-------------|---------|
-| 100 | 0.037ms | 0.008ms | 4.6× |
-| 500 | 0.061ms | 0.009ms | 7.2× |
-| 1,000 | 0.028ms | 0.004ms | 7.8× |
-| 2,000 | 0.043ms | 0.003ms | 13× |
-| 5,000 | 0.109ms | 0.003ms | **37×** |
-
-### N×N Visibility (AI "What can everyone see?")
-
-| Entity Count | O(n) approach | SpatialHash | Speedup |
-|--------------|---------------|-------------|---------|
-| 1,000 | 21ms | 1ms | 35× |
-| 2,000 | 85ms | 1ms | 87× |
-| 5,000 | 431ms | 2ms | **217×** |
-
-### When to Use Which Method
-
-| Use Case | Method | Complexity |
-|----------|--------|------------|
-| Nearby entities (AI, combat) | `grid.entities_in_radius(x, y, r)` | O(k) |
-| FOV-based visibility | `entity.visible_entities()` | O(n) + FOV |
-| All entities iteration | `for e in grid.entities` | O(n) |
-| Single cell lookup | `grid.at(x, y).entities` | O(n) filter |
-
----
-
-## Field of View & Visibility
-
-Entities track what they can see via `gridstate` - a per-cell record of visible and discovered states.
-
-### FOV Configuration
-
-```python
-# Grid-level FOV settings
-grid.fov = mcrfpy.FOV.SHADOW  # Algorithm (BASIC, DIAMOND, SHADOW, etc.)
-grid.fov_radius = 10           # Default view radius
-
-# Module-level default
-mcrfpy.default_fov = mcrfpy.FOV.PERMISSIVE_2
-```
-
-### Updating Visibility
-
-```python
-# Compute FOV from entity's position and update gridstate
-entity.update_visibility()
-
-# This also updates any ColorLayers bound via apply_perspective()
-```
-
-### Querying Visible Entities
-
-```python
-# Get list of other entities this entity can see (uses FOV + line-of-sight)
-visible_enemies = entity.visible_entities()
-
-# With custom FOV settings
-nearby = entity.visible_entities(radius=5)
-visible = entity.visible_entities(fov=mcrfpy.FOV.BASIC, radius=8)
-```
-
-**Note:** `visible_entities()` checks FOV and line-of-sight. For pure distance queries without FOV, use `grid.entities_in_radius()`.
-
-### Fog of War with ColorLayers
-
-```python
-# Create a ColorLayer for fog of war
-fov_layer = grid.add_layer('color', z_index=-1)
-fov_layer.fill((0, 0, 0, 255))  # Start black (unknown)
-
-# Bind to entity - layer auto-updates when entity.update_visibility() is called
-fov_layer.apply_perspective(
-    entity=player,
-    visible=(0, 0, 0, 0),           # Transparent when visible
-    discovered=(40, 40, 60, 180),    # Dark overlay when discovered
-    unknown=(0, 0, 0, 255)           # Black when never seen
-)
-
-# Now whenever player moves:
-player.x = new_x
-player.y = new_y
-player.update_visibility()  # Automatically updates the fog layer
-```
-
-### One-Time FOV Draw
-
-```python
-# Draw FOV without binding (useful for previews, spell ranges, etc.)
-fov_layer.draw_fov(
-    source=(player.x, player.y),
-    radius=10,
-    fov=mcrfpy.FOV.SHADOW,
-    visible=(255, 255, 200, 64),
-    discovered=(100, 100, 100, 128),
-    unknown=(0, 0, 0, 255)
-)
-```
-
-### Gridstate Access
-
-```python
-# Entity's per-cell visibility memory
-for state in entity.gridstate:
-    print(f"visible={state.visible}, discovered={state.discovered}")
-
-# Access specific cell state
-state = entity.at((x, y))
-if state.visible:
-    print("Entity can currently see this cell")
-elif state.discovered:
-    print("Entity has seen this cell before")
-```
-
-### GridPointState.point - Accessing Cell Data (#16)
-
-The `GridPointState.point` property provides access to the underlying `GridPoint` from an entity's perspective:
-
-```python
-state = entity.at((x, y))
-
-# If entity has NOT discovered this cell, point is None
-if not state.discovered:
-    print(state.point)  # None - entity doesn't know what's here
-
-# If entity HAS discovered the cell, point gives access to GridPoint
-if state.discovered:
-    point = state.point  # Live reference to GridPoint
-    print(f"walkable: {point.walkable}")
-    print(f"transparent: {point.transparent}")
-    print(f"entities here: {point.entities}")  # List of entities at cell
-```
-
-**Key behaviors:**
-- Returns `None` if `discovered=False` (entity has never seen this cell)
-- Returns live `GridPoint` reference if `discovered=True`
-- Changes to the `GridPoint` are immediately visible through `state.point`
-- This is intentionally **not** a cached copy - for historical memory, implement your own system in Python
-
----
-
-## EntityCollection
-
-`grid.entities` is an `EntityCollection` with list-like operations:
-
-```python
-# Add entities
-grid.entities.append(entity)
-grid.entities.extend([entity1, entity2, entity3])
-grid.entities.insert(0, entity)  # Insert at index
-
-# Remove entities
-grid.entities.remove(entity)
-entity = grid.entities.pop()  # Remove and return last
-entity = grid.entities.pop(0)  # Remove and return at index
-
-# Query
-count = len(grid.entities)
-idx = grid.entities.index(entity)
-n = grid.entities.count(entity)
-found = grid.entities.find("entity_name")  # Find by name
-
-# Iteration (O(n) - optimized in #159)
-for entity in grid.entities:
-    print(entity.pos)
-```
-
-### Iterator Performance (#159)
-
-EntityCollection iteration was optimized in commit 8f2407b:
-- **Before:** O(n²) due to index-based list traversal
-- **After:** O(n) using proper list iterators
-- **Speedup:** 103× at 2,000 entities
-
----
-
-## Entity Lifecycle
-
-### Creation
-
-```python
-# Basic creation
-entity = mcrfpy.Entity(pos=(10, 10), sprite_index=0)
-
-# With name for later lookup
-entity = mcrfpy.Entity(pos=(10, 10), sprite_index=0, name="player")
-```
-
-### Adding to Grid
-
-```python
-grid.entities.append(entity)
-# entity.grid is now set to grid
-# Entity is automatically added to SpatialHash for fast queries
-```
-
-### Movement
-
-```python
-# Direct position change (automatically updates SpatialHash)
-entity.pos = (new_x, new_y)
-
-# Animated movement
-mcrfpy.Animation("x", target_x, 0.3, "easeOutQuad").start(entity)
-mcrfpy.Animation("y", target_y, 0.3, "easeOutQuad").start(entity)
-
-# Update visibility after movement
-entity.update_visibility()
-```
-
-### Removal
-
-```python
-# Method 1: Remove from collection
-grid.entities.remove(entity)
-
-# Method 2: Entity.die() - removes from parent grid and SpatialHash
-entity.die()
-
-# After removal: entity.grid is None
-```
-
-### Transfer Between Grids
-
-```python
-def transfer_entity(entity, to_grid, new_pos):
-    """Move entity to a different grid."""
-    entity.die()  # Remove from current grid
-    entity.pos = new_pos
-    to_grid.entities.append(entity)
-```
-
----
-
-## Common Patterns
-
-### Player Entity with FOV
-
-```python
-class Player:
-    def __init__(self, grid, start_pos):
-        self.entity = mcrfpy.Entity(pos=start_pos, sprite_index=0, name="player")
-        grid.entities.append(self.entity)
-        
-        # Set up fog of war
-        self.fov_layer = grid.add_layer('color', z_index=-1)
-        self.fov_layer.fill((0, 0, 0, 255))
-        self.fov_layer.apply_perspective(
-            entity=self.entity,
-            visible=(0, 0, 0, 0),
-            discovered=(30, 30, 50, 180),
-            unknown=(0, 0, 0, 255)
-        )
-        self.entity.update_visibility()
-
-    def move(self, dx, dy):
-        new_x = self.entity.x + dx
-        new_y = self.entity.y + dy
-
-        point = self.entity.grid.at(new_x, new_y)
-        if point and point.walkable:
-            self.entity.pos = (new_x, new_y)
-            self.entity.update_visibility()  # Update FOV after move
-            return True
-        return False
-    
-    def get_visible_enemies(self):
-        """Get enemies this player can currently see."""
-        return [e for e in self.entity.visible_entities() 
-                if e.name and e.name.startswith("enemy")]
-```
-
-### Enemy AI with SpatialHash
-
-```python
-class Enemy:
-    def __init__(self, grid, pos, aggro_range=10):
-        self.entity = mcrfpy.Entity(pos=pos, sprite_index=1, name="enemy")
-        self.aggro_range = aggro_range
-        self.health = 100
-        self.grid = grid
-        grid.entities.append(self.entity)
-
-    def update(self):
-        # Use SpatialHash for efficient nearby entity detection
-        nearby = self.grid.entities_in_radius(
-            self.entity.x, self.entity.y, self.aggro_range
-        )
-        
-        # Find player in nearby entities
-        player = None
-        for e in nearby:
-            if e.name == "player":
-                player = e
-                break
-        
-        if player:
-            self.chase((player.x, player.y))
-        else:
-            self.wander()
-
-    def chase(self, target):
-        # Use pathfinding
-        path = self.entity.grid.find_path(
-            self.entity.x, self.entity.y, target[0], target[1]
-        )
-        if path and len(path) > 1:
-            next_cell = path[1]  # path[0] is current position
-            self.entity.pos = next_cell
-
-    def wander(self):
-        import random
-        dx = random.choice([-1, 0, 1])
-        dy = random.choice([-1, 0, 1])
-
-        new_pos = (self.entity.x + dx, self.entity.y + dy)
-        point = self.entity.grid.at(*new_pos)
-        if point and point.walkable:
-            self.entity.pos = new_pos
-```
-
-### Efficient Multi-Entity AI Loop
-
-```python
-def update_all_enemies(grid, enemies):
-    """Update all enemies efficiently using SpatialHash."""
-    for enemy in enemies:
-        # Each query is O(k) not O(n)
-        nearby = grid.entities_in_radius(enemy.x, enemy.y, enemy.aggro_range)
-        enemy.react_to_nearby(nearby)
-```
-
-### Item Entity
-
-```python
-class Item:
-    def __init__(self, grid, pos, item_type):
-        self.entity = mcrfpy.Entity(pos=pos, sprite_index=10 + item_type)
-        self.item_type = item_type
-        grid.entities.append(self.entity)
-
-    def pickup(self, collector):
-        """Called when another entity picks up this item."""
-        collector.inventory.append(self.item_type)
-        self.entity.die()  # Remove from grid
-```
-
-For more interaction patterns (click handling, selection, context menus), see [[Grid-Interaction-Patterns]].
-
----
-
-## Pathfinding
-
-Entities have built-in pathfinding via libtcod:
-
-```python
-# A* pathfinding to target (via Grid)
-path = grid.find_path(entity.x, entity.y, target_x, target_y)
-# Returns list of (x, y) tuples, or empty if no path
-
-if path:
-    next_step = path[1]  # path[0] is current position
-    entity.pos = next_step
-
-# Dijkstra for multi-target pathfinding
-grid.compute_dijkstra(goal_x, goal_y)
-distance = grid.get_dijkstra_distance(entity.x, entity.y)
-path = grid.get_dijkstra_path(entity.x, entity.y)
-```
-
-Pathfinding respects `GridPoint.walkable` properties set on the grid.
-
----
-
-## Performance Considerations
-
-### Current Performance (as of 2025-12-28)
-
-| Operation | Performance | Notes |
-|-----------|-------------|-------|
-| Entity Creation | ~90,000/sec | Sufficient for level generation |
-| Iteration | ~9M reads/sec | Optimized iterators (#159) |
-| Spatial Query | 0.003ms | SpatialHash O(k) (#115) |
-| N×N Visibility (5000) | 2ms | 217× faster than O(n) |
-
-### Recommendations
-
-1. **Use `entities_in_radius()` for AI** - O(k) queries instead of iterating all entities
-2. **Batch visibility updates** - Call `update_visibility()` once after all moves
-3. **Use timer callbacks for AI** - Don't run expensive logic every frame
-4. **Entity counts up to 5,000+** - SpatialHash makes large counts feasible
-
-### Internal Architecture
-
-- **SpatialHash:** Bucket-based spatial indexing (32-cell buckets)
-- **Automatic updates:** Hash updates on entity add/remove/move
-- **Weak references:** Hash doesn't prevent entity garbage collection
-
-See [[Performance-and-Profiling]] for detailed optimization guidance.
-
----
-
-## Related Systems
-
-- [[Grid-System]] - Spatial container for entities
-- [[Grid-Interaction-Patterns]] - Click handling, selection, context menus
-- [[Animation-System]] - Smooth entity movement
-- [[Performance-and-Profiling]] - Entity performance metrics
-
----
-
+# Entity Management
+
+Entities are game objects that implement behavior and live on Grids. While Grids handle rendering and mediate interactions, Entities encapsulate game logic like movement, combat, and AI.
+
+## Quick Reference
+
+**Parent System:** [[Grid-System]]
+
+**Key Types:**
+- `mcrfpy.Entity` - Game entities on grids
+- `mcrfpy.Grid` - Spatial container for entities
+- `mcrfpy.EntityCollection` - Collection of entities on a grid
+
+**Key Files:**
+- `src/UIEntity.h` / `src/UIEntity.cpp`
+- `src/UIEntityCollection.h` / `.cpp`
+- `src/SpatialHash.h` / `src/SpatialHash.cpp` - Spatial indexing
+
+**Related Issues:**
+- [#115](../issues/115) - SpatialHash for fast queries ✅ Implemented
+- [#117](../issues/117) - Memory Pool for entities (Deferred)
+- [#159](../issues/159) - EntityCollection iterator optimization ✅ Fixed
+
+---
+
+## What Are Entities?
+
+Entities are game objects that:
+- **Live on a Grid** (0 or 1 grid at a time)
+- **Have a sprite** for visual rendering
+- **Have grid position** (integer cell coordinates)
+- **Implement behavior** (movement, AI, combat, inventory)
+- **Track visibility** (which cells they can see / have seen)
+
+**Key distinction:** Entities implement behavior. Grids mediate interaction between entities and render them to screen.
+
+---
+
+## Entity-Grid Relationship
+
+The Entity-Grid relationship mirrors the UIDrawable parent-child pattern:
+
+| Relationship | Property | Automatic Behavior |
+|--------------|----------|-------------------|
+| Entity → Grid | `entity.grid` | Set when added to `grid.entities` |
+| Grid → Entities | `grid.entities` | Collection of all entities on grid |
+
+```python
+import mcrfpy
+
+# Create grid and entity
+grid = mcrfpy.Grid(grid_size=(50, 50), pos=(0, 0), size=(400, 400))
+player = mcrfpy.Entity(pos=(10, 10), sprite_index=0)
+
+# Before adding: entity has no grid
+print(player.grid)  # None
+
+# Add to grid
+grid.entities.append(player)
+
+# After adding: bidirectional link established
+print(player.grid == grid)  # True
+print(player in grid.entities)  # True
+
+# Removing breaks the link
+grid.entities.remove(player)
+print(player.grid)  # None
+```
+
+**Important:** An entity can only be on 0 or 1 grids at a time. Adding to a new grid automatically removes from the old one.
+
+---
+
+## Entity Properties
+
+### Position
+
+```python
+# Grid coordinates (integer cells)
+entity.x = 15
+entity.y = 20
+entity.pos = (15, 20)  # Tuple form
+
+# Draw position (float, for animation interpolation)
+print(entity.draw_pos)  # Actual render position
+```
+
+### Sprite
+
+```python
+entity.sprite_index = 5  # Index in texture sprite sheet
+```
+
+### Visibility
+
+```python
+entity.visible = True
+entity.opacity = 0.8  # 0.0 to 1.0
+```
+
+### Grid Reference
+
+```python
+current_grid = entity.grid  # Read-only, set by collection operations
+```
+
+---
+
+## Spatial Queries with SpatialHash
+
+As of commit 7d57ce2, grids use **SpatialHash** for efficient spatial queries. This provides O(k) query time where k is the number of nearby entities, instead of O(n) scanning all entities.
+
+### entities_in_radius()
+
+```python
+# Query entities within a radius (uses SpatialHash internally)
+nearby = grid.entities_in_radius(x, y, radius)
+
+# Example: Find all entities within 10 cells of position (50, 50)
+threats = grid.entities_in_radius(50, 50, 10)
+for entity in threats:
+    print(f"Entity at ({entity.x}, {entity.y})")
+```
+
+### Performance Comparison
+
+| Entity Count | O(n) Query | SpatialHash | Speedup |
+|--------------|------------|-------------|---------|
+| 100 | 0.037ms | 0.008ms | 4.6× |
+| 500 | 0.061ms | 0.009ms | 7.2× |
+| 1,000 | 0.028ms | 0.004ms | 7.8× |
+| 2,000 | 0.043ms | 0.003ms | 13× |
+| 5,000 | 0.109ms | 0.003ms | **37×** |
+
+### N×N Visibility (AI "What can everyone see?")
+
+| Entity Count | O(n) approach | SpatialHash | Speedup |
+|--------------|---------------|-------------|---------|
+| 1,000 | 21ms | 1ms | 35× |
+| 2,000 | 85ms | 1ms | 87× |
+| 5,000 | 431ms | 2ms | **217×** |
+
+### When to Use Which Method
+
+| Use Case | Method | Complexity |
+|----------|--------|------------|
+| Nearby entities (AI, combat) | `grid.entities_in_radius(x, y, r)` | O(k) |
+| FOV-based visibility | `entity.visible_entities()` | O(n) + FOV |
+| All entities iteration | `for e in grid.entities` | O(n) |
+| Single cell lookup | `grid.at(x, y).entities` | O(n) filter |
+
+---
+
+## Field of View & Visibility
+
+Entities track what they can see via `gridstate` - a per-cell record of visible and discovered states.
+
+### FOV Configuration
+
+```python
+# Grid-level FOV settings
+grid.fov = mcrfpy.FOV.SHADOW  # Algorithm (BASIC, DIAMOND, SHADOW, etc.)
+grid.fov_radius = 10           # Default view radius
+
+# Module-level default
+mcrfpy.default_fov = mcrfpy.FOV.PERMISSIVE_2
+```
+
+### Updating Visibility
+
+```python
+# Compute FOV from entity's position and update gridstate
+entity.update_visibility()
+
+# This also updates any ColorLayers bound via apply_perspective()
+```
+
+### Querying Visible Entities
+
+```python
+# Get list of other entities this entity can see (uses FOV + line-of-sight)
+visible_enemies = entity.visible_entities()
+
+# With custom FOV settings
+nearby = entity.visible_entities(radius=5)
+visible = entity.visible_entities(fov=mcrfpy.FOV.BASIC, radius=8)
+```
+
+**Note:** `visible_entities()` checks FOV and line-of-sight. For pure distance queries without FOV, use `grid.entities_in_radius()`.
+
+### Fog of War with ColorLayers
+
+```python
+# Create a ColorLayer for fog of war
+fov_layer = grid.add_layer('color', z_index=-1)
+fov_layer.fill((0, 0, 0, 255))  # Start black (unknown)
+
+# Bind to entity - layer auto-updates when entity.update_visibility() is called
+fov_layer.apply_perspective(
+    entity=player,
+    visible=(0, 0, 0, 0),           # Transparent when visible
+    discovered=(40, 40, 60, 180),    # Dark overlay when discovered
+    unknown=(0, 0, 0, 255)           # Black when never seen
+)
+
+# Now whenever player moves:
+player.x = new_x
+player.y = new_y
+player.update_visibility()  # Automatically updates the fog layer
+```
+
+### One-Time FOV Draw
+
+```python
+# Draw FOV without binding (useful for previews, spell ranges, etc.)
+fov_layer.draw_fov(
+    source=(player.x, player.y),
+    radius=10,
+    fov=mcrfpy.FOV.SHADOW,
+    visible=(255, 255, 200, 64),
+    discovered=(100, 100, 100, 128),
+    unknown=(0, 0, 0, 255)
+)
+```
+
+### Gridstate Access
+
+```python
+# Entity's per-cell visibility memory
+for state in entity.gridstate:
+    print(f"visible={state.visible}, discovered={state.discovered}")
+
+# Access specific cell state
+state = entity.at((x, y))
+if state.visible:
+    print("Entity can currently see this cell")
+elif state.discovered:
+    print("Entity has seen this cell before")
+```
+
+### GridPointState.point - Accessing Cell Data (#16)
+
+The `GridPointState.point` property provides access to the underlying `GridPoint` from an entity's perspective:
+
+```python
+state = entity.at((x, y))
+
+# If entity has NOT discovered this cell, point is None
+if not state.discovered:
+    print(state.point)  # None - entity doesn't know what's here
+
+# If entity HAS discovered the cell, point gives access to GridPoint
+if state.discovered:
+    point = state.point  # Live reference to GridPoint
+    print(f"walkable: {point.walkable}")
+    print(f"transparent: {point.transparent}")
+    print(f"entities here: {point.entities}")  # List of entities at cell
+```
+
+**Key behaviors:**
+- Returns `None` if `discovered=False` (entity has never seen this cell)
+- Returns live `GridPoint` reference if `discovered=True`
+- Changes to the `GridPoint` are immediately visible through `state.point`
+- This is intentionally **not** a cached copy - for historical memory, implement your own system in Python
+
+---
+
+## EntityCollection
+
+`grid.entities` is an `EntityCollection` with list-like operations:
+
+```python
+# Add entities
+grid.entities.append(entity)
+grid.entities.extend([entity1, entity2, entity3])
+grid.entities.insert(0, entity)  # Insert at index
+
+# Remove entities
+grid.entities.remove(entity)
+entity = grid.entities.pop()  # Remove and return last
+entity = grid.entities.pop(0)  # Remove and return at index
+
+# Query
+count = len(grid.entities)
+idx = grid.entities.index(entity)
+n = grid.entities.count(entity)
+found = grid.entities.find("entity_name")  # Find by name
+
+# Iteration (O(n) - optimized in #159)
+for entity in grid.entities:
+    print(entity.pos)
+```
+
+### Iterator Performance (#159)
+
+EntityCollection iteration was optimized in commit 8f2407b:
+- **Before:** O(n²) due to index-based list traversal
+- **After:** O(n) using proper list iterators
+- **Speedup:** 103× at 2,000 entities
+
+---
+
+## Entity Lifecycle
+
+### Creation
+
+```python
+# Basic creation
+entity = mcrfpy.Entity(pos=(10, 10), sprite_index=0)
+
+# With name for later lookup
+entity = mcrfpy.Entity(pos=(10, 10), sprite_index=0, name="player")
+```
+
+### Adding to Grid
+
+```python
+grid.entities.append(entity)
+# entity.grid is now set to grid
+# Entity is automatically added to SpatialHash for fast queries
+```
+
+### Movement
+
+```python
+# Direct position change (automatically updates SpatialHash)
+entity.pos = (new_x, new_y)
+
+# Animated movement
+mcrfpy.Animation("x", target_x, 0.3, "easeOutQuad").start(entity)
+mcrfpy.Animation("y", target_y, 0.3, "easeOutQuad").start(entity)
+
+# Update visibility after movement
+entity.update_visibility()
+```
+
+### Removal
+
+```python
+# Method 1: Remove from collection
+grid.entities.remove(entity)
+
+# Method 2: Entity.die() - removes from parent grid and SpatialHash
+entity.die()
+
+# After removal: entity.grid is None
+```
+
+### Transfer Between Grids
+
+```python
+def transfer_entity(entity, to_grid, new_pos):
+    """Move entity to a different grid."""
+    entity.die()  # Remove from current grid
+    entity.pos = new_pos
+    to_grid.entities.append(entity)
+```
+
+---
+
+## Common Patterns
+
+### Player Entity with FOV
+
+```python
+class Player:
+    def __init__(self, grid, start_pos):
+        self.entity = mcrfpy.Entity(pos=start_pos, sprite_index=0, name="player")
+        grid.entities.append(self.entity)
+        
+        # Set up fog of war
+        self.fov_layer = grid.add_layer('color', z_index=-1)
+        self.fov_layer.fill((0, 0, 0, 255))
+        self.fov_layer.apply_perspective(
+            entity=self.entity,
+            visible=(0, 0, 0, 0),
+            discovered=(30, 30, 50, 180),
+            unknown=(0, 0, 0, 255)
+        )
+        self.entity.update_visibility()
+
+    def move(self, dx, dy):
+        new_x = self.entity.x + dx
+        new_y = self.entity.y + dy
+
+        point = self.entity.grid.at(new_x, new_y)
+        if point and point.walkable:
+            self.entity.pos = (new_x, new_y)
+            self.entity.update_visibility()  # Update FOV after move
+            return True
+        return False
+    
+    def get_visible_enemies(self):
+        """Get enemies this player can currently see."""
+        return [e for e in self.entity.visible_entities() 
+                if e.name and e.name.startswith("enemy")]
+```
+
+### Enemy AI with SpatialHash
+
+```python
+class Enemy:
+    def __init__(self, grid, pos, aggro_range=10):
+        self.entity = mcrfpy.Entity(pos=pos, sprite_index=1, name="enemy")
+        self.aggro_range = aggro_range
+        self.health = 100
+        self.grid = grid
+        grid.entities.append(self.entity)
+
+    def update(self):
+        # Use SpatialHash for efficient nearby entity detection
+        nearby = self.grid.entities_in_radius(
+            self.entity.x, self.entity.y, self.aggro_range
+        )
+        
+        # Find player in nearby entities
+        player = None
+        for e in nearby:
+            if e.name == "player":
+                player = e
+                break
+        
+        if player:
+            self.chase((player.x, player.y))
+        else:
+            self.wander()
+
+    def chase(self, target):
+        # Use pathfinding
+        path = self.entity.grid.find_path(
+            self.entity.x, self.entity.y, target[0], target[1]
+        )
+        if path and len(path) > 1:
+            next_cell = path[1]  # path[0] is current position
+            self.entity.pos = next_cell
+
+    def wander(self):
+        import random
+        dx = random.choice([-1, 0, 1])
+        dy = random.choice([-1, 0, 1])
+
+        new_pos = (self.entity.x + dx, self.entity.y + dy)
+        point = self.entity.grid.at(*new_pos)
+        if point and point.walkable:
+            self.entity.pos = new_pos
+```
+
+### Efficient Multi-Entity AI Loop
+
+```python
+def update_all_enemies(grid, enemies):
+    """Update all enemies efficiently using SpatialHash."""
+    for enemy in enemies:
+        # Each query is O(k) not O(n)
+        nearby = grid.entities_in_radius(enemy.x, enemy.y, enemy.aggro_range)
+        enemy.react_to_nearby(nearby)
+```
+
+### Item Entity
+
+```python
+class Item:
+    def __init__(self, grid, pos, item_type):
+        self.entity = mcrfpy.Entity(pos=pos, sprite_index=10 + item_type)
+        self.item_type = item_type
+        grid.entities.append(self.entity)
+
+    def pickup(self, collector):
+        """Called when another entity picks up this item."""
+        collector.inventory.append(self.item_type)
+        self.entity.die()  # Remove from grid
+```
+
+For more interaction patterns (click handling, selection, context menus), see [[Grid-Interaction-Patterns]].
+
+---
+
+## Pathfinding
+
+Entities have built-in pathfinding via libtcod:
+
+```python
+# A* pathfinding to target (via Grid)
+path = grid.find_path(entity.x, entity.y, target_x, target_y)
+# Returns list of (x, y) tuples, or empty if no path
+
+if path:
+    next_step = path[1]  # path[0] is current position
+    entity.pos = next_step
+
+# Dijkstra for multi-target pathfinding
+grid.compute_dijkstra(goal_x, goal_y)
+distance = grid.get_dijkstra_distance(entity.x, entity.y)
+path = grid.get_dijkstra_path(entity.x, entity.y)
+```
+
+Pathfinding respects `GridPoint.walkable` properties set on the grid.
+
+---
+
+## Performance Considerations
+
+### Current Performance (as of 2025-12-28)
+
+| Operation | Performance | Notes |
+|-----------|-------------|-------|
+| Entity Creation | ~90,000/sec | Sufficient for level generation |
+| Iteration | ~9M reads/sec | Optimized iterators (#159) |
+| Spatial Query | 0.003ms | SpatialHash O(k) (#115) |
+| N×N Visibility (5000) | 2ms | 217× faster than O(n) |
+
+### Recommendations
+
+1. **Use `entities_in_radius()` for AI** - O(k) queries instead of iterating all entities
+2. **Batch visibility updates** - Call `update_visibility()` once after all moves
+3. **Use timer callbacks for AI** - Don't run expensive logic every frame
+4. **Entity counts up to 5,000+** - SpatialHash makes large counts feasible
+
+### Internal Architecture
+
+- **SpatialHash:** Bucket-based spatial indexing (32-cell buckets)
+- **Automatic updates:** Hash updates on entity add/remove/move
+- **Weak references:** Hash doesn't prevent entity garbage collection
+
+See [[Performance-and-Profiling]] for detailed optimization guidance.
+
+---
+
+## Related Systems
+
+- [[Grid-System]] - Spatial container for entities
+- [[Grid-Interaction-Patterns]] - Click handling, selection, context menus
+- [[Animation-System]] - Smooth entity movement
+- [[Performance-and-Profiling]] - Entity performance metrics
+
+---
+
 *Last updated: 2025-12-28*
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