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 frozen apartments.
He attacks my firing a beam that creates a clump of crystals, which he then shatters by braking apart and swinging into it. He also tries to crush the player by making repeated jumps.
He starts out purple but changes from that to Pink, then finally to yellow. After his corporeal form is destroyed, he can be captured via trap like any sub-boss.