Is changing weaknesses from 200% damage to 150% damage an easy hack? This might be advisable if Oil is too strong in 1.40.
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Moving [Haste and Shell] down to 8 MP also puts them on the same level with Yell (which I still believe needs Regen), which either could be the better ability depending on the situation. (Example, do you want a 100% Add: Haste ability that isn't reflectable and is instant with no AOE? Or do you want a possibly slightly inaccurate spell that has a small AOE but is reflectable and requires a short charge time?)
The only tanky caster I can think of is maybe Oracle, and even then I don't think high movement suits them that well.
[We] could add a Talk Skill that could add Reflect maybe MA + 65% of the time or something.
Speaking of Move, I feel that Summoners should also be bumped to 4 Move and be given access to knives. Low HP, high MP, high Move support caster is something that appeals to me. I know that this suggestion is rather unorthodox, but so is a lot of Arena in comparison to other patches and especially vanilla.