Marel-Xyx
The gods as arrogant as ever decided to challenge humanity, ever so confident in their success. If the gods won, they exterminated humanity once and for all. If humanity won, they could make one wish.
13 Challenges, made for the purpose of extinction. However, humanity was clever. With both sides on a stand still, the final challenger won. Humanity won, they made their wish. But this wish wasn't for their own benefit. It was the gods demise.
Every 10 years, the gods were forced to inhabit mortal bodies for 3 years. Humanities memories of this disappeared. Their decision by vote was to randomize the order in which 13 gods entered the mortal plane.
But to enter the world as a mortal was a painful process in which they inhabited a recent dead body that fits themselves.
They have to navigate the world that they discarded, fighting against monsters for survival. Waiting to reclaim their godhood.