I was able to do the same, but the first 2 round end stupidly quickly with all my abilities, and since i'm using my debuffs for them too, sphinx ends up with no debuffs throughout most of the battle, and since i'm using Arthur w/ sniper shot instead of mordred or a healer with bp/cleanse, I could die pretty fast but... managed to pull it off in auto ability. but honestly it just takes longer, but at least i know i can do it.. i'll stick with auto 1-2 and auto ability 3 cause it's just faster, and i'm lazy