Marvel vs DC
Connection:
Both are extremely powerful comic book villains who are the antithesis of beings who represent the multiverse with (Eternity and Monitor respectively). These forces of darkness would battle against reality itself, but are shown as being on the seeming back foot compared to their counterparts (Chaos King having to hide his identity for a long time and Anti-Monitor only having a single part of the Antimatter Universe) at first. This would soon change as their secret machinations went into ahead with both launching a full scale assault on the universe (Chaos War and Crisis on Infinite Earths respectively) with dark perversions of some of their enemies (The resurrected gods and the shadow demons who have sometimes shown to be doppelgangers of the heroes).
Both of them would also gain the help of other villains, usually giving them something in return (Chaos King reviving Abomination to help him find death and Anti-Monitor recruiting the Psycho-Pirate to help mess with the Monitors team in return of giving him his own world to mess with)
However both would be stopped by the combined forces of gods amped by several individuals (Hercules and Spectre respectively) as well as a villain only helping out because they kind of had to (Galactus and Darkseid respectively) alongside a force of several other heroes and villains across the universe. Though despite this failure, both would manage to destroy most of the infinite multiverse (Chaos King destroyed 98% of the multiverse while Anti Monitor destroyed all but three of the infinite Earths).
Both also mainly wanted to destroy the multiverse because it gave them a domain to rule over
Both of them also have other names that aren't as well known in and out of universe (Amatsu-Mikaboshi and Mobius respectively)
Later on, the two would be revealed to be pawns used by far larger and much darker gods who were also orchestrating several other events in their reality (Oblivion and Perpetua respectively)
