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

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Rattle's Undertale Smash Or Pass by Saturn-Domo on DeviantArt

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Free PC Pinball, a lot of game mods, etc.

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