Sans is a major character from Undertale, the 2015 indie game that became a huge source of remix culture online. The default dance part of the meme comes from Fortnite's hugely recognizable dance emote, which spread across gaming edits in the late 2010s. Combining the two created a simple crossover joke that fit YouTube compilations, Discord posts, and short-form video edits. It still gets reused because people instantly recognize both references, and the contrast between Sans's laid-back image and a flashy dance remains funny.