So, I know I'm triple posting and that's rude, but I'm really curious...
What do you guys think the dragon replacement will be? Or do you think I'm going to use dragons as well?
In place of dragons? You might use wyrms, scaly/plated things that burrow through the ground with ease and little trace, like in Dune or Tremors, or even the Hobbit: BoFA. A doom that gives little to no warning, and leaves obvious traces of destruction, or just drags everything underground.
I'm also cool with using Blarog's instead of Dragons. Or really any other supernatural champion or scourge of the mortal realms.
We could also borrow Alien... just sayin' that's a pretty iconic enemy there.
Or perhaps something far more iconic, a variant on Syrens. Powerful and beautiful beings served by fanatic thralls, not easily intimidated or faced, except by the most resolute wills. They often send minions/young to neighboring countries as ambassadors, and within a few centuries once glorious empires are now merely puppet states. Their natural beauty, prevents most from lifting a blade or spell against them, yet most not already in their clutches fear the reach and might of the Syrens.
Just a few thoughts, since you asked. :)