I also keep a couple bar-element spells in my macro bar when I'm doing the final ACP mission for a few reasons:
+ .5 second casting time means it's more likely to get off without being interrupted by draw in.
+ With a quick casting time, rotating through a few of them should keep you at cap for a higher percentage of the time than if you were just using dispel and blind
+ Having the corresponding barspell up for the nuke the crystal is casting might make you ever-so-slightly more likely to get a half-resist if your stunner misses.
Note that this is only for bar-element spells (barstone, barwater, etc.) and not the bar-status spells, which take forever to cast. The main minus is that there's no CE on barspells, and the MP:VE ratio is worse than Blind as well as Poison:
Blind: VE - 640 MP - 9 VE/MP - 71 Casting time - 2.00
Poison: VE - 320 MP - 5 VE/MP - 64 Casting time - 1.00
Barstone: VE - 300 MP - 6 VE/MP - 50 Casting time - 0.50
This is really just a situational toy though, useful in this fight because of the short casting time. For anything else, either Dispel, Blind, Sleep or a Job Ability will always be up.
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