Electro Koopa

Electrikoopa was an enemy Koopa first seen in Super Mario Sunshine. They threw their shells at you like a boomerang in an attempt to shock you, and succeeding in doing so meant 1 point of damage. To kill them, you could either stomp on the vulnerable Koopa inside while the shell was out for 1 coin, or you could spray the vulnerable Koopa with FLUDD to have the shell come back and shock the Koopa for multiple coins. Or, you could just eat it with Yoshi.