Does your world have any powerful characters who are locked away?

My example would be the wolf spirit, Risluva.

He is basically my own version of Fenrir.

In the old legends of my world, it is foretold that Risluva is "The Hound Who Will Eat The Stars." Basically this means that should he ever reach his true power, he will shroud the universe in darkness and signal the beginning of the end of all creation.

Risluva isn't just a being who helps end the world. He is The beginning of the end. The universe cannot canonically reach its end until he attains his true power. Luckily for the universe, various fragments of his power are bound behind the very souls of multiple gods.

Not to mention that he can't even exist in the physical world without being summoned, and the only way to summon him is with a one-of-a-kind grimoire that every world religion hates with a burning passion.

I really like my apocalypse puppy :)