Adding a self defense mechanism to the Companion Cube was widely regarded as a bad idea. That didn’t stop Aperture Science. Meet the antagonist of Portal 3.
Although, come to think of it, it wouldn’t be much of a boss fight. It’s not like the Cube could taunt you, lie to you, beg for mercy or run away.
(via Stabby Companion Cube by ~Ankhareon on deviantART)