UnderFell is an Alternate Universe created by fans. The main idea of it is everyone is their cruel counterparts, and apparently only wear orange, black, and red.
by DepressingVoice16 March 27, 2016
The Edgy Angry Alternate Universe Counterpart To Papyrus. He's more popular than that cool skeleton and has all the girls, such as Akari.
Akari stopped as Underfell Papyrus loomed over her, an angry expression on his face as usual
by Rainy Melai October 27, 2017
The edgy version of the hit classic game undertale which involves some changes to the story as flowey is kind in the story.

The human stays in the underground as the adopted child of the king in the true ending after defeating their final boss.
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Abby: Underfell has a sans with a gold tooth. No further infromation about it.
Sandy: Aw, that is very sad indeed.
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by Retardost December 13, 2021