"Megalovania" (also stylized as "MeGaLoVania" and "MEGALOVANIA") is a frequently ripped track composed by Toby Fox. It is a major meme on the SiIvaGunner channel, and a sub-meme of Undertale.
The song was first composed by Toby "Radiation" Fox for the EarthBound Halloween Hack, a hack of the SNES game EarthBound. It was mainly inspired by the song "Megalomania" from the SNES J-RPG Live A Live by composer Yoko Shimomura, as he originally intended to directly use that song for his hack but encountered technical difficulties.
Toby Fox remixed the song a few years later for the webcomic Homestuck, for which he was a composer.[1] The song first appeared in the Flash game Alterniabound in a secret room, before making a proper debut in the animation "[S] Wake".
The song is best known as Sans's boss theme in the game Undertale, created and composed by Toby Fox himself.[2]
Following the immediate success and critical acclaim of Undertale online, "Megalovania" became one of the most popular songs from the game, receiving millions on views on YouTube across dozens of different versions. This song would receive a new arrangement made by Toby Fox for Super Smash Bros. Ultimate's Sans Mii costume in the Ver. 5.0.0 update.