Primus Underfell - An Undertale Fangame by Primus Official - Game Jolt

Best Undertale Games - Game Jolt

Primus Underfell - An Undertale Fangame by Primus Official - Game Jolt

Primus!Underfell - Papyrus by Nerveabhorrence on DeviantArt

Underfell (Team Spritedgy) Pre-Demo (Genocide)

Undertale Rejuvenation, UNDERTALE Fangame

Stream [UndertaleAU] Swapfell - Flowey Incorporated by Jason Sixty Four {MOVED}

Undertale Yellow on Android : r/UndertaleYellow

Underswap Wiki

Overtale, Undertale AU Wiki

UNDERFELL Development update #2

Undertale Skin: Underfell Sans (Primus) Minecraft Skin

Best Undertale Games - Game Jolt

HALLOWEEN UPDATE] The Reveal - Primus Underfell - An Undertale Fangame by Atrea [Primus]

Información sobre el Fan-game de Underfell y Swapfell

Did anyone knew about this easter egg? My friend found this. We've done some researches but couldn't find anything so we are asking for reddit's help : r/Undertale