Megalovania is a track by Toby Fox that became widely known through the 2015 game Undertale, where it plays during the Sans battle. The song quickly spread far beyond the game because its opening notes are so recognizable and easy to use as a punchline. Online, it became shorthand for extreme difficulty, surprise danger and “final boss” comedy. It still shows up in meme edits, gaming clips and parody videos because listeners instantly understand the joke as soon as the melody starts.