Mordekaiser would inevitably Aatrox

As a previous post before me has pointed out: Aatrox is a dragon.

Viego, a being much weaker than Mordekaiser, is very much capable of enslaving dragons. This leaves out his capacity to enslave/coerce Aspects given his interaction with Pantheon in the 2021 Ruination event.

Given that Mordekaiser can tank existence erasure in the Death Realm, he should be relatively immune to whatever Aatrox can dish out (given Aatrox is not fighting a physical avatar in Runeterra).

So the battle would devolve into Mordekaiser trying to enslave Aatrox until he succeeds (given what Viego did, this should be easily done).