Undertale - no one is safe from sans's trolling........not even sans

So he's pranking himself across time and space too? Damn.

Time travel in fiction seems to work on various levels. One way is the “Back to the Future” way where, yes, affecting stuff in the past affects the existing future timeline.

Another is the “everything is set in stone” method where it’s like “by going into the past to stop Hitler you inadvertently help him come into power, meaning nothing changes.”

Then you’ve got the “Zelda” method where split timelines exist. In Zelda’s case the splits are all localized to Ocarina of Time. “Adult Timeline” is the world after Ganondorf seven years into in the future is defeated by an older Link and Zelda and sealed away. Later leads into Wind Waker where he somehow breaks the seal. “Child Timeline” where Link, after finishing the future business, went back seven years to before he even met Zelda, warned Zelda of Ganondorf’s impended treachery, she told the king, Ganondorf sentenced to death for treason, execution fails because of divine fate that cannot be changed, and then the events of Twilight Princess happen. Lastly is “Hero defeated” where we get a timeline where Ganondorf actually did manage to kill OoT Link and thus continued to rule Hyrule. This later leads to a war that sets up the events of A Link to the Past.

(yeah I know I got super wordy on the Zelda part)