As a sort of challenge to myself, I decided to make a creature capable of ravaging worlds; at least, I hope it can.
Half-Dragon Spellwarped Tarrasque Bloodscale Fury 12 with the Passion's Flame Sovereign Archetype (I'm aware it can't actually take the archetype... unless it can. Haven't read those rules in a while.)
It has, among other things, Cleric casting with a CL of 48. It is almost impossible to kill in a straight-on fight.
Oh, and it has an intelligence of 9, so it can plan...
(I'm really thinking about throwing on that feat that gives Alter Form as a (Su) ability to dragons only. As well as spellfire. And maybe a level of Binder...)