The Pump Chimera is another version of the Multiple Chimeras. It is rarely seen in the game. It only comes out to help Lucas and Boney get one of the Seven Needles by draining a pool of water. It then shoots it out somewhere. Afterwards, it quickly returns back to the lab.
The Pump Chimera only appears in Mother 3. He is the only Chimera that will help you, though two other ones could help you if needed. He is not violent, like one of his brothers the Ultimate Chimera, and will only do his job. It was created by Dr. Andonuts for Porky. You never see him after the beginning of Chapter 7, until the credits.