diff --git a/dev-assets/doodads/bird/bird.js b/dev-assets/doodads/bird/bird.js
new file mode 100644
index 0000000..ca8db3e
--- /dev/null
+++ b/dev-assets/doodads/bird/bird.js
@@ -0,0 +1,54 @@
+// Red bird mob.
+function main() {
+	var speed = 4;
+	var Vx = Vy = 0;
+	var altitude = Self.Position().Y; // original height in the level
+
+	console.log("Bird altitude is %d", altitude);
+
+	var direction = "left";
+	var states = {
+		flying: 0,
+		diving: 1,
+	};
+	var state = states.flying;
+
+	Self.SetMobile(true);
+	Self.SetGravity(false);
+	Self.SetHitbox(0, 10, 46, 32);
+	Self.AddAnimation("fly-left", 100, ["left-1", "left-2"]);
+	Self.AddAnimation("fly-right", 100, ["right-1", "right-2"]);
+
+	Events.OnCollide(function(e) {
+		if (e.Actor.IsMobile() && e.InHitbox) {
+			return false;
+		}
+	});
+
+	// Sample our X position every few frames and detect if we've hit a solid wall.
+	var sampleTick = 0;
+	var sampleRate = 2;
+	var lastSampledX = 0;
+	var lastSampledY = 0;
+
+	setInterval(function() {
+		if (sampleTick % sampleRate === 0) {
+			var curX = Self.Position().X;
+			var delta = Math.abs(curX - lastSampledX);
+			if (delta < 5) {
+				direction = direction === "right" ? "left" : "right";
+			}
+			lastSampledX = curX;
+		}
+		sampleTick++;
+
+		// TODO: Vector() requires floats, pain in the butt for JS,
+		// the JS API should be friendlier and custom...
+		var Vx = parseFloat(speed * (direction === "left" ? -1 : 1));
+		Self.SetVelocity(Vector(Vx, 0.0));
+
+		if (!Self.IsAnimating()) {
+			Self.PlayAnimation("fly-"+direction, null);
+		}
+	}, 100);
+}
diff --git a/dev-assets/doodads/bird/dive-left.png b/dev-assets/doodads/bird/dive-left.png
new file mode 100644
index 0000000..4ec5794
Binary files /dev/null and b/dev-assets/doodads/bird/dive-left.png differ
diff --git a/dev-assets/doodads/bird/dive-right.png b/dev-assets/doodads/bird/dive-right.png
new file mode 100644
index 0000000..8516ae3
Binary files /dev/null and b/dev-assets/doodads/bird/dive-right.png differ
diff --git a/dev-assets/doodads/bird/left-1.png b/dev-assets/doodads/bird/left-1.png
new file mode 100644
index 0000000..e3c6e50
Binary files /dev/null and b/dev-assets/doodads/bird/left-1.png differ
diff --git a/dev-assets/doodads/bird/left-2.png b/dev-assets/doodads/bird/left-2.png
new file mode 100644
index 0000000..e093f1f
Binary files /dev/null and b/dev-assets/doodads/bird/left-2.png differ
diff --git a/dev-assets/doodads/bird/right-1.png b/dev-assets/doodads/bird/right-1.png
new file mode 100644
index 0000000..91930e2
Binary files /dev/null and b/dev-assets/doodads/bird/right-1.png differ
diff --git a/dev-assets/doodads/bird/right-2.png b/dev-assets/doodads/bird/right-2.png
new file mode 100644
index 0000000..380b3b3
Binary files /dev/null and b/dev-assets/doodads/bird/right-2.png differ
diff --git a/dev-assets/doodads/build.sh b/dev-assets/doodads/build.sh
index 784a47c..d9d7f8a 100755
--- a/dev-assets/doodads/build.sh
+++ b/dev-assets/doodads/build.sh
@@ -98,6 +98,17 @@ azulians() {
 	cd ..
 }
 
+mobs() {
+	cd bird/
+
+	doodad convert -t "Bird (red)" left-1.png left-2.png right-1.png right-2.png \
+		dive-left.png dive-right.png bird-red.doodad
+	doodad install-script bird.js bird-red.doodad
+
+	cp *.doodad ../../../assets/doodads/
+	cd ..
+}
+
 objects() {
 	cd objects/
 
@@ -136,14 +147,38 @@ onoff() {
 	cd ..
 }
 
+warpdoor() {
+	cd warp-door/
+
+	doodad convert -t "Warp Door" door-1.png door-2.png door-3.png door-4.png warp-door.doodad
+	doodad edit-doodad -q --tag color=none warp-door.doodad
+	doodad install-script warp-door.js warp-door.doodad
+
+	doodad convert -t "Warp Door (Blue)" blue-1.png blue-2.png blue-3.png blue-4.png blue-off.png \
+		warp-door-blue.doodad
+	doodad edit-doodad -q --tag color=blue warp-door-blue.doodad
+	doodad install-script warp-door.js warp-door-blue.doodad
+
+	doodad convert -t "Warp Door (Orange)" orange-off.png orange-1.png orange-2.png orange-3.png orange-4.png \
+		warp-door-orange.doodad
+	doodad edit-doodad -q --tag color=orange warp-door-orange.doodad
+	doodad install-script warp-door.js warp-door-orange.doodad
+
+	cp *.doodad ../../../assets/doodads/
+
+	cd ..
+}
+
 boy
 buttons
 switches
 doors
 trapdoors
 azulians
+mobs
 objects
 onoff
+warpdoor
 doodad edit-doodad -quiet -lock -author "Noah" ../../assets/doodads/*.doodad
 doodad edit-doodad -hide ../../assets/doodads/azu-blu.doodad
 doodad edit-doodad -hide ../../assets/doodads/boy.doodad
diff --git a/dev-assets/doodads/on-off/blue-button.png b/dev-assets/doodads/on-off/blue-button.png
index 184627a..9df37be 100644
Binary files a/dev-assets/doodads/on-off/blue-button.png and b/dev-assets/doodads/on-off/blue-button.png differ
diff --git a/dev-assets/doodads/on-off/blue-off.png b/dev-assets/doodads/on-off/blue-off.png
index 6275e2b..1375fe6 100644
Binary files a/dev-assets/doodads/on-off/blue-off.png and b/dev-assets/doodads/on-off/blue-off.png differ
diff --git a/dev-assets/doodads/on-off/blue-on.png b/dev-assets/doodads/on-off/blue-on.png
index e200231..20cc9ba 100644
Binary files a/dev-assets/doodads/on-off/blue-on.png and b/dev-assets/doodads/on-off/blue-on.png differ
diff --git a/dev-assets/doodads/on-off/orange-button.png b/dev-assets/doodads/on-off/orange-button.png
index ec5ef16..fbf2cde 100644
Binary files a/dev-assets/doodads/on-off/orange-button.png and b/dev-assets/doodads/on-off/orange-button.png differ
diff --git a/dev-assets/doodads/on-off/orange-off.png b/dev-assets/doodads/on-off/orange-off.png
index 1ce8f1e..e2fa95e 100644
Binary files a/dev-assets/doodads/on-off/orange-off.png and b/dev-assets/doodads/on-off/orange-off.png differ
diff --git a/dev-assets/doodads/on-off/orange-on.png b/dev-assets/doodads/on-off/orange-on.png
index c56e09e..0aaae44 100644
Binary files a/dev-assets/doodads/on-off/orange-on.png and b/dev-assets/doodads/on-off/orange-on.png differ
diff --git a/dev-assets/doodads/on-off/state-block-blue.js b/dev-assets/doodads/on-off/state-block-blue.js
index f09f5cc..b754ea7 100644
--- a/dev-assets/doodads/on-off/state-block-blue.js
+++ b/dev-assets/doodads/on-off/state-block-blue.js
@@ -1,6 +1,6 @@
 // Blue State Block
 function main() {
-	Self.SetHitbox(0, 0, 33, 33);
+	Self.SetHitbox(0, 0, 42, 42);
 
 	// Blue block is ON by default.
 	var state = true;
diff --git a/dev-assets/doodads/on-off/state-block-orange.js b/dev-assets/doodads/on-off/state-block-orange.js
index dfea8b7..8989f73 100644
--- a/dev-assets/doodads/on-off/state-block-orange.js
+++ b/dev-assets/doodads/on-off/state-block-orange.js
@@ -1,6 +1,6 @@
 // Orange State Block
 function main() {
-	Self.SetHitbox(0, 0, 33, 33);
+	Self.SetHitbox(0, 0, 42, 42);
 
 	// Orange block is OFF by default.
 	var state = false;
diff --git a/dev-assets/doodads/on-off/state-button.js b/dev-assets/doodads/on-off/state-button.js
index 85084d8..c5e7bd7 100644
--- a/dev-assets/doodads/on-off/state-button.js
+++ b/dev-assets/doodads/on-off/state-button.js
@@ -5,7 +5,7 @@ var state = false;
 
 function main() {
 	console.log("%s ID '%s' initialized!", Self.Title, Self.ID());
-	Self.SetHitbox(0, 0, 33, 33);
+	Self.SetHitbox(0, 0, 42, 42);
 
 	// When the button is activated, don't keep toggling state until we're not
 	// being touched again.
diff --git a/dev-assets/doodads/warp-door/blue-1.png b/dev-assets/doodads/warp-door/blue-1.png
new file mode 100644
index 0000000..4921faf
Binary files /dev/null and b/dev-assets/doodads/warp-door/blue-1.png differ
diff --git a/dev-assets/doodads/warp-door/blue-2.png b/dev-assets/doodads/warp-door/blue-2.png
new file mode 100644
index 0000000..ca96abf
Binary files /dev/null and b/dev-assets/doodads/warp-door/blue-2.png differ
diff --git a/dev-assets/doodads/warp-door/blue-3.png b/dev-assets/doodads/warp-door/blue-3.png
new file mode 100644
index 0000000..1a1e75c
Binary files /dev/null and b/dev-assets/doodads/warp-door/blue-3.png differ
diff --git a/dev-assets/doodads/warp-door/blue-4.png b/dev-assets/doodads/warp-door/blue-4.png
new file mode 100644
index 0000000..f676890
Binary files /dev/null and b/dev-assets/doodads/warp-door/blue-4.png differ
diff --git a/dev-assets/doodads/warp-door/blue-off.png b/dev-assets/doodads/warp-door/blue-off.png
new file mode 100644
index 0000000..a42b51c
Binary files /dev/null and b/dev-assets/doodads/warp-door/blue-off.png differ
diff --git a/dev-assets/doodads/warp-door/door-1.png b/dev-assets/doodads/warp-door/door-1.png
new file mode 100644
index 0000000..e057d24
Binary files /dev/null and b/dev-assets/doodads/warp-door/door-1.png differ
diff --git a/dev-assets/doodads/warp-door/door-2.png b/dev-assets/doodads/warp-door/door-2.png
new file mode 100644
index 0000000..71d0b61
Binary files /dev/null and b/dev-assets/doodads/warp-door/door-2.png differ
diff --git a/dev-assets/doodads/warp-door/door-3.png b/dev-assets/doodads/warp-door/door-3.png
new file mode 100644
index 0000000..d225a8d
Binary files /dev/null and b/dev-assets/doodads/warp-door/door-3.png differ
diff --git a/dev-assets/doodads/warp-door/door-4.png b/dev-assets/doodads/warp-door/door-4.png
new file mode 100644
index 0000000..65f3e03
Binary files /dev/null and b/dev-assets/doodads/warp-door/door-4.png differ
diff --git a/dev-assets/doodads/warp-door/orange-1.png b/dev-assets/doodads/warp-door/orange-1.png
new file mode 100644
index 0000000..01a6a61
Binary files /dev/null and b/dev-assets/doodads/warp-door/orange-1.png differ
diff --git a/dev-assets/doodads/warp-door/orange-2.png b/dev-assets/doodads/warp-door/orange-2.png
new file mode 100644
index 0000000..2bb01fb
Binary files /dev/null and b/dev-assets/doodads/warp-door/orange-2.png differ
diff --git a/dev-assets/doodads/warp-door/orange-3.png b/dev-assets/doodads/warp-door/orange-3.png
new file mode 100644
index 0000000..1983e86
Binary files /dev/null and b/dev-assets/doodads/warp-door/orange-3.png differ
diff --git a/dev-assets/doodads/warp-door/orange-4.png b/dev-assets/doodads/warp-door/orange-4.png
new file mode 100644
index 0000000..f8c08b2
Binary files /dev/null and b/dev-assets/doodads/warp-door/orange-4.png differ
diff --git a/dev-assets/doodads/warp-door/orange-off.png b/dev-assets/doodads/warp-door/orange-off.png
new file mode 100644
index 0000000..476703a
Binary files /dev/null and b/dev-assets/doodads/warp-door/orange-off.png differ
diff --git a/dev-assets/doodads/warp-door/warp-door.js b/dev-assets/doodads/warp-door/warp-door.js
new file mode 100644
index 0000000..2dc73ab
--- /dev/null
+++ b/dev-assets/doodads/warp-door/warp-door.js
@@ -0,0 +1,81 @@
+// Warp Doors
+function main() {
+	console.log("Warp Door %s Initialized", Self.Title);
+
+	Self.SetHitbox(0, 0, 34, 76);
+
+	// Are we a blue or orange door? Regular warp door will be 'none'
+	var color = Self.GetTag("color");
+	var isStateDoor = color === 'blue' || color === 'orange';
+	var state = color === 'blue';  // Blue door is ON by default.
+
+	var animating = false;
+	var collide = false;
+
+	// Declare animations and sprite names.
+	var animSpeed = 100;
+	var spriteDefault, spriteDisabled;  // the latter for state doors.
+	if (color === 'blue') {
+		Self.AddAnimation("open", animSpeed, ["blue-2", "blue-3", "blue-4"]);
+		Self.AddAnimation("close", animSpeed, ["blue-4", "blue-3", "blue-2", "blue-1"]);
+		spriteDefault = "blue-1";
+		spriteDisabled = "blue-off";
+	} else if (color === 'orange') {
+		Self.AddAnimation("open", animSpeed, ["orange-2", "orange-3", "orange-4"]);
+		Self.AddAnimation("close", animSpeed, ["orange-4", "orange-3", "orange-2", "orange-1"]);
+		spriteDefault = "orange-1";
+		spriteDisabled = "orange-off";
+	} else {
+		Self.AddAnimation("open", animSpeed, ["door-2", "door-3", "door-4"]);
+		Self.AddAnimation("close", animSpeed, ["door-4", "door-3", "door-2", "door-1"]);
+		spriteDefault = "door-1";
+	}
+
+	console.log("Warp %s: default=%s  disabled=%+v  color=%s  isState=%+v  state=%+v", Self.Title, spriteDefault, spriteDisabled, color, isStateDoor, state);
+
+	// Subscribe to the global state-change if we are a state door.
+	if (isStateDoor) {
+		Message.Subscribe("broadcast:state-change", function(newState) {
+			console.log("Warp %s: received state to %+v", Self.Title, newState);
+			state = color === 'blue' ? !newState : newState;
+
+			// Activate or deactivate the door.
+			Self.ShowLayerNamed(state ? spriteDefault : spriteDisabled);
+		});
+	}
+
+	// TODO: respond to a "Use" button instead of a Collide to open the door.
+	Events.OnCollide(function(e) {
+		if (!e.Settled) {
+			return;
+		}
+
+		if (animating || collide) {
+			return;
+		}
+
+		// Only players can use doors for now.
+		if (e.Actor.IsPlayer() && e.InHitbox) {
+			if (isStateDoor && !state) {
+				// The state door is inactive (dotted outline).
+				return;
+			}
+
+			// Play the open and close animation.
+			animating = true;
+			collide = true;
+			Self.PlayAnimation("open", function() {
+				e.Actor.Hide()
+				Self.PlayAnimation("close", function() {
+					Self.ShowLayerNamed(isStateDoor && !state ? spriteDisabled : spriteDefault);
+					e.Actor.Show()
+					animating = false;
+				});
+			});
+		}
+	});
+
+	Events.OnLeave(function(e) {
+		collide = false;
+	});
+}
diff --git a/pkg/uix/actor.go b/pkg/uix/actor.go
index cc16527..72ef702 100644
--- a/pkg/uix/actor.go
+++ b/pkg/uix/actor.go
@@ -37,6 +37,7 @@ type Actor struct {
 	hasGravity bool
 	isMobile   bool // Mobile character, such as the player or an enemy
 	noclip     bool // Disable collision detection
+	hidden     bool // invisible, via Hide() and Show()
 	hitbox     render.Rect
 	inventory  map[string]int    // item inventory. doodad name -> quantity, 0 for key item.
 	data       map[string]string // arbitrary key/value store. DEPRECATED ??
@@ -117,6 +118,12 @@ func (a *Actor) IsMobile() bool {
 	return a.isMobile
 }
 
+// IsPlayer returns whether the actor is the player character.
+// It's true when the Actor ID is "PLAYER"
+func (a *Actor) IsPlayer() bool {
+	return a.Canvas.Name == "PLAYER"
+}
+
 // Size returns the size of the actor, from the underlying doodads.Drawing.
 func (a *Actor) Size() render.Rect {
 	return a.Drawing.Size()
@@ -157,6 +164,16 @@ func (a *Actor) SetGrounded(v bool) {
 	a.grounded = v
 }
 
+// Hide makes the actor invisible.
+func (a *Actor) Hide() {
+	a.hidden = true
+}
+
+// Show a hidden actor.
+func (a *Actor) Show() {
+	a.hidden = false
+}
+
 // SetNoclip sets the noclip setting for an actor. If true, the actor can
 // clip through level geometry.
 func (a *Actor) SetNoclip(v bool) {
diff --git a/pkg/uix/canvas_actors.go b/pkg/uix/canvas_actors.go
index ce8f6ad..5bb02e3 100644
--- a/pkg/uix/canvas_actors.go
+++ b/pkg/uix/canvas_actors.go
@@ -113,6 +113,12 @@ func (w *Canvas) drawActors(e render.Engine, p render.Point) {
 			log.Error("Canvas.drawActors: null actor at index %d (of %d actors)", i, len(w.actors))
 			continue
 		}
+
+		// Skip hidden actors.
+		if a.hidden {
+			continue
+		}
+
 		var (
 			can        = a.Canvas // Canvas widget that draws the actor
 			actorPoint = a.Position()