Megalovania was composed by Toby Fox and first appeared in earlier projects before becoming famous as the Sans boss theme in Undertale, released in 2015. Its fast, relentless riff matched the difficulty and tone of that fight, helping the track spread far beyond the game through remixes, covers, and memes. Short clips of the opening became a shared shorthand online for an impending challenge or dramatic turn, which keeps this brief version in constant use for edits, streams, and gaming videos.