The meme centers on Sans, the fan-favorite skeleton from Undertale, a 2015 indie game by Toby Fox. Online editors began using clips of Sans performing the Fortnite default dance as a crossover joke, mixing Undertale fandom with a widely recognized gaming emote. The format spread through reposts, short edits and meme compilations because the contrast is instantly readable even without context. It still gets used when creators want a quick absurdist punchline built around game culture and unexpected character animation.