Sans and Flowey (spoiler)

Question

Careful : This question and the possible answers contain spoilers about the all the endings of Undertale. Don't go further if you do not want to be spoiled.

After you have completed the neutral ending one time, you can reload the game at the barrier and start another fight with Asgore. After defeating him, you can have some additional dialogs with Flowey.

During one of those, Flowey says the following sentence, referring to Papyrus's brother :

You know. Smiley Trashbag.

...

Say. If I have ONE piece of advice for you... DON'T. Let his brother. Find out ANYTHING about you. He'll... well... Let's just say. He's caused me more than my fair share of resets. Stay away from that guy.

It seems like, reading this sentence, that Sans already fought and beat Flowey many times in the past. But, during the whole game, it doesn't seems like Sans has ever met Flowey at all. Is there any evidence in the game other than this dialogue which would confirm a fight between the two characters, like a book, a dialogue, or anything ?

Answer 1

Unmarked spoilers ahead (since spoiler warnings are included in the question).

It seems like, reading this sentence, that Sans already fought and beat Flowey many times in the past. But, during the whole game, it doesn't seems like Sans has ever met Flowey at all.

Both these statements are true. Flowey has the ability to Save and Load.

After acquiring this ability, Flowey first tried to help the denizens of the Underground but got bored and began messing with and killing them. The resets he mentioned were caused by him being discovered by and defeated by Sans.

Sans is aware something keeps reseting the timeline but, unlike Flowey, cannot Save and does not keep memories of other timelines. He doesn't know of Flowey's identity (or perhaps even his existence) in any timeline in-game.

Answer 2

Sans is well aware of Flowey for he can bend space and time. As Flowey kills everybody Sans stops him like he tried to do with you in the Genocide run. Sans could not allow that to happen so he had to kill Flowey knowing well enough that Flowey can just reset his save file -- that's why while fighting Sans he says "Even if we do... we'll just end up back here. Right?"

He is saying that even if he kills you, you can just reload your save file. Besides the fact that Sans may not remember some things from different timelines, he can still travel through time. Each timeline is a new Sans but all the Sans' that exist are not aware of each other, however they can all travel through each timeline.

This makes it the same Sans for when you are trying to get Sans' room key. Each time there is a new Sans the reason why he knows how many times you died is because you are in the same timeline. If you change it Sans will still travel to your timeline -- meaning he will know how many times you have died.

To sum it all up Sans knows who Flowey is and he knows what you are doing in Genocide because he saw Flowey do it. As Sans fights you he tries to break your determination like he did with Flowey, but your determination is stronger than Flowey's. Thus, Sans has killed Flowey many times and because of this Flowey gave up after awhile.

Answer 3

There is the theory that Sans was, or is, a human, and that would explain why he had caused Flowey his fair share of resets. Because Sans is already powerful as a monster, and as a human, he would be unstoppable. Or, maybe Sans sought out Flowey, for papyrus. In Grillby's, Sans says that Papyrus meets a talking flower. Now, we all know he is referring to Flowey. But what if Sans got sick of Papyrus telling him this, and went to find Flowey himself, and found out about his plan to destroy humanity. We don't know which timeline this is in, and it could have been when any of the souls passed through, and he killed Flowey six times, one for every soul. Now, this is just a theory, and is could not be true, but I hope it helps!