godot-physics

Assign each object a collision_layer bit for what it is and a collision_mask for what it detects. Layer 1 equals value 1, layer 4 equals value 8, so detecting layers 4 and 6 means setting the mask to 8 | 32, or using set_collision_mask_value(4, true).

Use an Area2D for the bullet, set its collision_layer to the projectile layer and its collision_mask to the enemy body layer bit. Connect the body_entered signal to detect CharacterBody2D enemies, or area_entered for other Area2D hitboxes.

CharacterBody2D handles manual movement with move_and_slide and collision responses like is_on_floor, suited for players and enemies. Area2D only detects overlaps through signals and is used for bullets, pickups, triggers, and hitboxes.

The Area2D collision_mask must include the player's collision_layer bit, and the body_entered signal must be connected. Also verify the player uses a physics body type like CharacterBody2D, since body_entered does not fire for other Area2D nodes.

Enable one_way_collision on the CollisionShape2D of a StaticBody2D platform. The player then falls through from below but lands on top, which is the standard pattern for platformer levels.