The 'Sans in Smash' meme refers to the legendary moment during a September 2019 Nintendo Direct when Sans from Undertale was revealed as a Mii Gunner costume for Super Smash Bros. Ultimate. For years, fans had campaigned and joked about Sans joining the roster, often considering it an impossible dream. The reveal, accompanied by a special remix of Megalovania by Toby Fox, sent shockwaves through the gaming community. This meme is used to celebrate unexpected victories, express shock at unbelievable crossovers, or simply to evoke the chaotic energy of Undertale's most famous skeleton appearing in a major AAA title.