UNITALE Flowey Genocide Fight 

me

Lol

Nightbot thanks

You just spare him like any other monster. Kinda boring.

That's not true. I think that was a glitch or something. I've actually done a proper spare ending now.

I did it. He takes your soun and crashes the game

And it's called that due to its use on the unity engine

No its a mod

Depends on how you look at it. Is it in UNDERTALE? No, but there is this downloadable game called UNITALE, where people can make fan made battles, and you can download them, and try them out. This is one of the Fan-Made battles.

um can i ask what is it exactly is like a game editing program or something or is it its own game?

Unitale is it's own game. Somebody has remade the Undertale battle system, and made it moddable, so people who know programming can make their own fights. You should check it out: reddit.com/r/unitale/