You have to fill a box or chest or something like that with garbage and throw it on the head of your enemies.
But how do you do it? It says something like "no space" when I try to place the object.
you have to put it close to the character, not directly on top. just move around and release right when it turns from red to white. also note that you can rotate it with the mouse wheel before dropping. the damage seems to be weight/2, so yeah, not worth it on higher levels damage-wise, but can still be useful for blocking, and telekinesis just costs 1ap. i used to always carry 2 of those 10k 150kg metal boxes on Beast.
