Monster suggestions?

Heya! Sorry I keep posting about my campaign, but I think I got it!

So the premise is a 3.5e cr 90 ancient time dragon has lived to 5.5 and is basically a god chilling at the end of time. It's laid an egg, and sent it back to DND time so it can incubate properly.

The other gods are not cool with this, and send the party to destroy it, protecting them from being killed in the past by it, while the Wyrm weaponizes the butterfly effect against them, rewriting history to make things harder for the party.

Furthermore, it starts religions based on it in the past, depowering the gods so they can't mess with it more. It also has a couple warlocks running around, and dragonflesh abominations.

Its egg is kept in a reliquary in a cathedral to itself, with the final boss of the campaign being a non-human monster who's made a deal and become time pope, but I don't know what monster that would be

(The Wyrm also gets comuppence at the end, DW)