Godot 3d tutorial: https://docs.godotengine.org/en/stable/getting_started/first_3d_game/07.killing_player.html

Mob.gd

@@ -0,0 +1,27 @@
+extends CharacterBody3D
+
+@export var min_speed = 10
+@export var max_speed = 18
+
+signal squashed
+
+func _physics_process(delta):
+	move_and_slide()
+	
+func initialize(start_position, player_position):
+	# Look to the player
+	look_at_from_position(start_position, player_position, Vector3.UP)
+	# But rotate a little bit
+	rotate_y(randf_range(-PI / 4, PI / 4))
+	# Set random speed
+	var random_speed = randi_range(min_speed, max_speed)
+	# Apply the velocity
+	velocity = Vector3.FORWARD * random_speed
+	velocity = velocity.rotated(Vector3.UP, rotation.y)
+	
+func squash():
+	squashed.emit()
+	queue_free()
+
+func _on_visibility_notifier_screen_exited():
+	queue_free()