In the Earthbound Halloween ROM Hack, with the Dr. Andonuts bossfight.
MeGaLoVania, the Homestuck version featuring Vriska's guitars, first shows up in the flash animation [S] Wake.
Mainly considered to be Aradia's theme though instead of Vriska's, and the Homestuck Megalovania is the better version look it up, but the entire Homestuck OST is so f**king good with over 500 songs, so you could look it up and listen to it
You will not regret it