Sans

Sans is a skeleton hailing from the faraway dimension of Undertale. He is very humerus.

Skeleton of Revenge
Sans is a skeleton that just up and appeared one day in the monster world, nobody knowing where he came from or who he was there.

A boy would later appear and make a few shenanigans with the timeline while Sans watched him or something.

Season 4
However, Sans managed to build his machine and and returned the the place he once came from.

Despite nobody knowing or recognizing him, Sans claims to be very familiar with The Final Rumble and it's people. ESPECIALLY a certain agent. Now, Sans joins TFR mostly for fun since he isn't much fond of wrestling, or at least, that's what he wants people to believe.

Episode 3
Now, tired of being a lazy bones, Sans is concerned about someone as strong as the boy wherever he came from showing up, and decided to join a group of investigators to find out more.

However, it didn't turn out very well, as this body of hirs is pure bones.