I'm on board for the GEO crystal changing Cleric Stance to something else. It'd be tough to come up with a suitable replacement, but here's some suggestions:

If you want to use it for MP management, turn it into a toggle where using spells cost less and refund MP per use but causing you to deal a less damage.

Another option would be give spells certain effects depending on whether you're in not-cleric-stance or not. It would make stance-dancing a main mechanic of GEO but I figure someone out there might like it.

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Ground target AOE shouldn't be a main mechanic of GEO, but its lv50 ability should be something along those lines to stay within concept.