The Crystarobo is a brutish crystalline sub-boss in the form of rock-like moving crystals. It was captured by the Ghostbusters while on the loose in Fr'ozen A'partments.
He attacks by firing a beam that creates a clump of crystals, which he then shatters by braking apart and swinging into it. Don't bother firing at the crystals - aim for the head to do the most damage. He also tries to crush the player by making repeated jumps; when you're cornered, crouch and crawl or he'll stomp you.
He starts out purple but with damage, he changes to Pink, then finally to yellow. After his corporeal form is destroyed, he can be captured via trap like any sub-boss.