Baxter Stockman designed these robotic mice, the Mobile Offensive Underground Search Excavation and Retrieval Sentries (M.O.U.S.E.R.S.) to infiltrate the sewers. Their small size makes them ideal for finding hidden passageways in and out of banks, power stations, and other secure areas. Stockman controls them with a pheromone spray and hopes to increase his wealth and power by terrorizing New York with his creations. But the Turtles make short work of them whenever they meet.