Castle Mendheim: Double Secret power-up
Detonate the Nuke in the big open area and look around to find a "Double Secret" power-up. Use this to blast away your opponents in the rest of the level. Combine this enhancement with some Magnum for easy one shot kill destruction. You may need to refill Magnum to keep this up, but you can get an unlimited supply. The number of shots needed to exterminate enemies varies based on the difficulty selected and the tank strength, which is determined in the team alignment screen.