Goyen - Crimson Desert

Kliff is sent to the Abyss after he's been corrupted to seek out a mentor who can help enlighten him. He meets a mysterious old man named Goyen, who forces him to spar and strengthen his resolve, before disappearing, once Kliff overcomes and proves he has the will to keep going. Kliff is obviously confused who this old man is. In the post-game, Kliff read the Axiom Archive where >!It is revealed he has been set in an infininte time loop set by the Guardians, every time he fails to stop Umbra, they rewind time and adjust the world to get a different outcome. He was forced to do this 108 cycles until he finally won. Goyen is the 45th attempt of Kliff, where the world ended but he surived the End and was trapped in the abyss trapped to never live or die and he watched cycles after him come and go. He finally found peace and died after Kliff #108 broke the cycle!<

Nameless Puppet - Lies of P

When Pinnochio stands up against his father and refuses his heart, Geppetto summons a horrifying grotesque zombie puppet simply called the Nameless Puppet to kill Pinnochio. If you read all the notes and clues from previous dialogue, it 99.9% likely the Namless Puppet was Carlo, Pinnochio's rotting corpse from his previous life when he was a reality boy 

The astronaut - Zathura

Zach and Walter summon an astronaut in the board game to help them survive. It is revealed that he is actually Walter grown up and trapped in the game when he wished Zach never existed and couldn't finish the game without another player 

A character is revealed to be a future/past version of the protagonist (Bonus points if the protagonist never finds out)