CHRISTIAN GOD VERSUS CATHOLIC HOLY SPIRIT
TEUTONIC HORNED ONE VERSUS KALI
MOHAMMED VERSUS ZEUS
(although you couldn't put a progression ladder for one-player in it, or else you'd anger so many religions you could basically just assume you'd be marked for death)
so I guess just round-robin it, and after you've beat every fighter with every other fighter, that's "the end"
ultimate metaphysical armageddon, all-inclusive ragnarok