In many walkthroughs for SoM, they always want you to do complicated stuff when it comes to killing the second to last boss, the Dark Lich. Instead, just have a couple fairie walnuts and when the Dark Lich appears, just start pummeling him with the Lumina spell. Right after you cast it, keep checking on when you can use another one of the girl's spells. When her spells become active again, use the Lumina again. Repeat. If the girl's MP gets low, have the Sprite use a fairie walnut on her. If all goes well, you should be able to defeat the Dark Lich without getting a scratch and before he even has a chance to do anything!
