As you battle with your Chunky, it will gain experience each time it defeats another Chunky. Your Chunky's level will then be determined by how much experience it has. Each time your Chunky levels up, its stats will increase by a small amount making it stronger in battles. There will be certain level milestones that Chunkies will reach and be rewarded with a new move it can use in battle or even evolve! When your Chunky is ready to evolve it will transform into a new, stronger form of itself.