I've figured out my own boss battle style, here it is! ATTACKING Every so often an attack button will appear in a random part of the screen. Touch it and press Z to attack! If you've played my RPG engine, you now how to heal yourself when you fight the slime. This will be the same for big boss battles. You will always have the chance to mercy, it will always be there. Acting, i'm sorry, I don't think I will add that to my style, sorry :(.
Credit to LucasBro for the slash animation! Credit to Undertale for sans and their attacking sounds! And the heart.
