Seriously, Evrae, noted as the hardest storyline boss went down like a complete ***** in my game, I suppose Hastega+Slow is a lethal combination, but to be honest, I didn't even need it, the only attack that kind of messed me up was Poison Breath, but nothing one of my 99+ Al Bhed Potions couldn't fix up. Sinspawn Gui couldn't handle one shot of Fira on its arms or other areas, so it went down quick, have yet to fight Seymoar Flux yet on the Remaster, but I assume it won't be very hard.
Hell, I beat Anima and Seymoar with Shiva alone.
I wonder how tough Seymoar at Mt Gagazet will be, he was a nightmare for me as a child.