Nuclear Power Pants is a monster you battle in Adventure Mode. It is found in The Rad-Lands.
When has stomping randomly *not* solved all you problems? Clear of the danger you continue on, heading to the central lab - if the final MacGuffin had to be somewhere, it'd probably be there. Before long, you come across a poorly segue'd setup to the next boss - it's just a pair of Nuclear Power Pants walking on the road towards you. Have fun!