So! I just found a CLEAR reference to Undertale in Smash Ultimate - Super Smash Bros. Ultimate Forum - Neoseeker Forums

So, I've been binging smash ultimate since it come out. And the only Challenge i have left to complete is the 200 quickpl

Super sans Bros Ultimate Modpack [Super Smash Bros. Ultimate] [Mods]

Guide to beating 'The True Arena' (Guide Completed!) (Spoiler Free

Every Undertale Reference in the Sans Reveal Trailer for Super

Super sans Bros Ultimate Modpack [Super Smash Bros. Ultimate] [Mods]

Guide to beating 'The True Arena' (Guide Completed!) (Spoiler Free

Ness? [Super Smash Bros. Ultimate] [Mods]

Ness? [Super Smash Bros. Ultimate] [Mods]

Ness? [Super Smash Bros. Ultimate] [Mods]

WarioWare Gold FAQ v0.99 - Neoseeker Walkthroughs

Promoting game > Smash Bros x Undertale officially exists > Ash