It's been way too long. Sorry if I'm rusty with this! Original song: Bonetrousle (Undertale OST, by Toby Fox) In truth, the only reason I settled on making this specifically an AoSTH mashup was because Bonetrousle and Robotnik's theme from the show are both in the same key, C-Minor. EDIT 19 JAN 2018: If you just stumbled on this video while searching Undertale, Bonetrousle or the like, I have a lot of other videos which (at least in my view) are more entertaining and well-edited than this. Give them a look if you enjoyed this one.