Koopa Troopa Stack
From the Super Mario Wiki
Koopa Troopa Stacks are a type of enemy appearing in Paper Mario: Color Splash. A stack of Koopa Troopas form when multiple Koopa Troopas group up, forming a stack. They only appear as a 6-Stack, and their health is represented by the number of Koopa Troopas left in the stack. Koopa Troopa Stacks appear on Lighthouse Island and in the Green Energy Plant.