This strategy is pretty cool. Basically, you daze with Thunder and chain attack to poison with Riki. Normally, Gonzalez will use his Craze aura at 50% HP, but I got so lucky that I managed to interrupt him (you can see for a few frames that he started casting the art, I even stopped thinking from the shock). After the chain attack you have to survive until the next one, so equip as much defense as you can. His Craze aura gives him immunity to Daze. You won't have filled Dunban's talent art by then (unless you have Final Flicker, which I didn't want to use because technically you don't have it at level 40), but I wanted to chain attack to Shield Dunban so he can survive a little more. He might kill you if he double attacks, which happens often. If you manage to survive, you do a second chain attack (after Craze ends) and finish it (or keep surviving until you win, but that's tough because he uses stronger arts than before). Also you'll need to daze him if a vision is going to kill you.
In order to hit with Thunder, you need to link Enlightenment from Melia, which increases ether arts accuracy. Also level Thunder at least to level 5. I'm not sure about the accuracy modifier on arts, it's either (Art level * 5) or 5 if level less than 5, 25 if level 5 or more (that's what I got from different sources). So either way, level it up to at least level 5 to be safe. It's not guaranteed to hit but it has decent accuracy.
Porque no te afecta el aura de corrosión? Esa mecánica es mu molesta, como la evitas en toda la pelea?
Oh gosh that ending was too perfect. "Riki likes fighting easy monsters."
Apparently in DE the arts get accuracy bonuses all the way up to 12, in original they only got accuracy bonuses up to 5.