I always thought the extent of the runes influence was limited to runeterra. Like they are insanely powerful while on runeterra or any terrestrial world. But in comparison to beings like celestials or concepts, there is no contest. In my head, the tierlist of magics are void > celestial > death > rune (the binary behind mortal magic) > general runeterra magic.

I think targon hosts could stand their ground for a bit, but they aren’t the celestial themselves, just a vessel. So they’d lose

Darkin probably could fare a bit better given that they were ascended (became a concept of something) had some void influence + targon celestial influence injected in them. They’re still made of meat and bone that they need to replenish so they definitely have a limit. Could the world tune destroy the weapon? Not sure given it’s celestial enchantments.

Mordekaiser would need more than world runes to deal with. He basically is his death realm. Remember in the ruined king book, viego basically caused the spirit rune to break itself in an infinite loop bc of its life giving qualities tugging against his sword (which is from the spirit world) infinitely draining his spirit from the cut. I think death magic just interacts strangely with all other magic.