Kill plane

A kill plane is an invisible boundary in a game level that instantly kills or respawns the player when touched. Kill planes are typically placed under the playable area to catch when the player falls and prevent them from falling infinitely.

From a level design perspective, kill planes are safety nets. They can be infinite and cover the entire level at once or be specific to certain areas like lava pits where the character burns up on contact.

You can use them to respawn the player at the beginning of the level, the last checkpoint, or at the edge of the platform they fell from.

We commonly place kill planes below platforms in platformers, race tracks in racing games, or at the bottom of pits and cliffs.

In Godot, you can implement kill planes using an area node with a world boundary shape. The WorldBoundaryShape2DWorldBoundaryShape2D creates an infinite line that detects collisions on one side, while WorldBoundaryShape3DWorldBoundaryShape3D creates an infinite plane for 3D games. Then you can detect when the player enters the area like any other area node:

extends Area2D

func _ready():
	body_entered.connect(func (body: Node) -> void:
		if body is Player:
			body.die()
	)

This approach is more efficient than using large collision boxes as world boundary shapes are infinite and only check collisions from one direction. They're optimized for this use case. If you need a kill plane that is smaller than the entire level, you can use a regular area node with a rectangle or box collision shape instead.