create bubble environmental particle

objects/environment/bubble/bubble.gd

@@ -0,0 +1,22 @@
+extends Area2D
+
+export var speed = 16.0
+
+onready var sprite = $Sprite
+
+var lifetime = 0.0
+
+func _ready():
+	sprite.frame_coords.x = randi() % sprite.hframes
+
+func _physics_process(delta):
+	lifetime += delta
+	if speed > 0.0:
+		sprite.position.x = sin(lifetime * 4.0) * 4.0
+	position.y -= speed * delta
+
+func _on_area_entered(area):
+	if area.is_in_group("player") or area.is_in_group("arrow"):
+		sprite.frame_coords.y = 1
+		speed = 0.0
+		get_tree().create_timer(0.5, false).connect("timeout", self, "queue_free")

objects/environment/bubble/bubble.tscn

@@ -0,0 +1,20 @@
+[gd_scene load_steps=4 format=2]
+
+[ext_resource path="res://graphics/particles/bubble.png" type="Texture" id=1]
+[ext_resource path="res://objects/environment/bubble/bubble.gd" type="Script" id=2]
+
+[sub_resource type="RectangleShape2D" id=1]
+extents = Vector2( 2, 2 )
+
+[node name="Bubble" type="Area2D"]
+script = ExtResource( 2 )
+
+[node name="Sprite" type="Sprite" parent="."]
+texture = ExtResource( 1 )
+hframes = 4
+vframes = 2
+
+[node name="CollisionShape2D" type="CollisionShape2D" parent="."]
+shape = SubResource( 1 )
+
+[connection signal="area_entered" from="." to="." method="_on_area_entered"]