For the last portion of the fight, a third spell card called "Scion of Harmony" (?) can go along with the "Scion of Spirits" and "Scion of Elements" cards
because, not only for 'balance rep' but it goes along with the story—the harmony of the two forces, light and shadow.
--you could do one astral attack, a shadow attack, and then a balance attack just to get the sense of "harmony" and continuity with the other choices.
