Super Mario 128

Each Mario is extremely easy to defeat (Birdo will give you a tougher time), but there are a lot of them. Use a character such as Donkey Kong, Mario, Yoshi, Bowser, or Link to hit lots of them at once with a spin attack. Marth, Roy, and Mr. Game and Watch are also good choices. Sometimes, the Marios might accidentally KO each other with their own attacks.