mega whipermon

whipermon plus

whipermon

ES stands for evolution stone. You evolve a monster horstie-horstie plus-mega horstie. Or katsuya plus-mega katsuya. you start  buying ESs in Cactus. Also, in the train going to Timber, Connor gives you an ES. Your starter monster evolves. When a monster evolves, it changes color and gains a new skill.