[quote=@Burthstone]
<Snipped quote by Silver Fox>

Fine then, it's Frisk possessed by Chara's theme song.

But it doesn't really fit as Sans' theme.
[/quote]

I think it's fits fine once you piss him off. 

Which to be fair, took quite a bit of effort.

Otherwise, I like his other two themes that fit with his laid back ness