Hamster

This is an enemy that Steve and Ron encounter on Bowser's airships through out their playthrough of Super Mario Bros. 3. In Episode 5 of the Pixel Brains playthrough of Super Mario Bros. 3, Ron calls this enemy a hamster. Steve corrects him, saying they are actually Beavers (they're actually Moles).

These enemies hide under manhole covers, then spring out and throw wrenches.