honesty, I have it pretty easy considering i found amon U like...right before the event, lol ...

beat ragnarok Sphinx in all of a few turns..

1- 45% def debuff, 20% atk debuff , 20% atk buff+ normal attack twice (she's almost raging, and ready for overdrive atk)
2- eligos ability (raging) amon U ability (half rage bar down) + arthurs ability + eligos 3rd and beelzebub rampage was enough to make her stunned in 1 turn
3- still rampage, attack her and she turns out to still be stunned after it, so used amon U stunned ability after.. but didn't work lol
4- she's literally almost dead. but uses her normal overdrive atk and kills..2? of my kami.. while the rest are now at full burst from the high damage, and i just auto abilitied from there..

no real strategy, just purely offense, i didn't expect to win but i actually did lol