It was the hardest fight in NA at the moment (that before was Kiara/Kama full buffs/full gauge), to do without Command Seals/revive or Artoria Caster so I'm glad I managed
You need:
- 2 Arjuna's Alter buster cards on turn 1 to break the first bar
- activate guts 3 times with S. Orion (Koyanskaya cooldown reduction + Anniversary Blond MC) because Cernunnos too thick lol