Genji Glove+Offering still works, but he has high evasion and defense so it won't come close to a one hit kill. It's going to be a long process, but I think that Omega will be tough without resorting to weakening of characters.
The Offering relic ignores enemy evasion stats.

20 Ragnaroks? How do you allocate enough space to insert the script? Maybe you're replacing a monster that originally had a long script.