Started playing blind, and now I'm down to everything except a few Colosseum wagers, secrets missing from the WOB and the entire Kefka tower thing, which I'm honestly fine with, I can discover the secrets latter.
However, concerning Gau here, I'm finding out that I'm missing the Kudzu and Locust rages - you just spend so very little time outside Esper Mountain that IMO, it doesn't make sense to not have an island in the WoR where you can find said rages. Same for formations like Stray Cat, Raven or WoB permanently missable formations. He's such a fantastic source of cheap AOE damage with Io and Behemoth, and a nice nuker with 3X Attack rages and the Bone Club/Power Glove. I just find it a bit irksome how I'm missing these two just because I didn't hang around Esper Mountain enough, I guess.
As for Esper builds, I went 50/50. Gau certainly appreciates the speed, but since the guy is really damn frail I found myself going for Stray just to enable Gau to dodge all the magic crap thrown at him. Overall, a very enjoyable character, I just would like if he was a lot less random - maybe add a way in later updates so you can control at least what Gau is targeting or what attack he's using? Or maybe a way to switch Rages - all three of these are fine options and I would be fine with any of them excluding each other - after all, we don't Gau to break open the game, but a bit of reliability for boss fights like Hidon, Wrexsoul would go a long way. IMO, just enabling him to target something would go a long way.