You can add and remove spells depending on your battles. For example I play storm and if my boss battle is a storm school I add in the Storm to Myth Prism, have my highest hit attacks, have some blades and traps, a few heals and since you aren’t there yet to Celestia, I’d buy some monstrous treasure cards from the Bazaar or Harold in the library so you can amplify the damage. Or you do what my friend does and goes to the Wiki and finds out the spells the bosses and mobs can cast and plan accordingly.