Undertale: Thanatos!

MT EBOTT. 202X Legends say that those who climb the mountain never return. You, as the new fallen human, possess the power to manipulate the world. But your actions have shown such power can easily corrupt your mind. Your own curiosity, resulted in a mass extinction. Repeating the same events over and over again. But nothing is meant to last forever. Your very own power has consumed you. And now consequences of your actions are finally crawling up your back. Are you ready?

Long ago, two races ruled over Earth: HUMANS and MONSTERS. One day, war broke out between the two races. After a long battle, the humans were victorious. They sealed the monsters underground with a magic spell.