Use the arrow keys to navigate, Z to select/proceed through text and X to go back. When attacking, press Z when as close to the middle as you can. If your heart (soul) is yellow during an attack, press Z to shoot. Blue rays are harmless, white rays are dangerous. Press the green flag to restart the battle.
Thanks to @pococikapusta for the battle creator. Undertale belongs to Toby Fox. Pokemon belongs to Nintendo. Music - Mewtwo Battle (Pokemon X & Y)