Olaf is a snowman from the movie Frozen, he is a one-off character in this video, being a guest star and allowing Anime Chara and Nathan to dismember him.
Olaf once again appears with demented red eyes in Attack of the one-offs. Underfell Sans, Underfresh Sans, and Classic Anime Chara appear too, attacking Anime Chara.
Olaf has a demented counterpart in the Frozen Wiki, that eats feces.
Olaf was the best choice for dismemberment in the series as he is a snowman and can't feel pain.
It is unknown if Olaf puts himself back together after the episode is done, But the answer is most likely "No" because he was torn apart beyond repair.
There is no hints of an Elsa in Anime Chara's timeline, so it is unknown how Olaf is alive. It may be an Olaf from another timeline where Elsa exists.
Olaf talks in a derpy voice, To make him seem dumb and less smart than he actually is in the movie.
The red eyes in Attack of the one-offs are based off of a .EXE character, since Olaf is an innocent movie character and innocent characters are ruined by Sonic.EXE fangames.