In terms of needs, I need none of them. I've got every class reasonably covered.
I'm leaning towards LAlter (Story-locked/Arturia option), Marie (Rider/Starter option), and Parvati (Costume option)
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Challenge Quest line-up: Illya, Eggplant, Support Merlin, Beebs, Fran, Herc.
I let Illya nuke Arjuna (MLB Kaleidoscope and 1 command seal), let Arash nuke himself as the support Merlin Invulned everyone. Then let everyone beatdown Bryn and JAlter. Barely survived as JAlter hits like a Mac Truck.