New spells will become available after defeating each of the bosses. You can spend Dessert Points to enhance each spell’s damage, area-of-effect, and potency. You can only upgrade the spells you have unlocked. MP is required to activate Ultimate Spells. You can recover your MP naturally by collecting Desserts. You can also pick up blue potions dropped by enemies or purchased from the shop.
Like passive skills, spells are attached to weapons. However, spells can be swapped forcibly to a random one as a negative effect from scrolls dropped by mid-bosses or those purchased from shops or as part of a selected game mode’s mechanic. The Custom Loadout game mode gives you the freedom to select any weapon and ultimate spell you have unlocked so far.