From Bulbapedia, the community-driven Pokémon encyclopedia.
Little Battle is a special rule used in Pokémon Battle Revolution, unlocked after beating Mysterial and can be played in Sunny Park Colosseum. It differs very little from a standard knockout battle besides the fact that the Pokémon used must all be at or below level 5 and must be the lowest form of their evolution family as well as be able to evolve. Moves that deal a fixed amount of damage such as SonicBoom are banned. These rules make it almost an updated version of Pokémon Stadium 2's Little Cup. It is designed to test the Trainer's Pokémon breeding skills.