A colleague of mine introduced me to this mashup by Isosine this winter:
I think it works as an example of a really well-put together basic mashup. The music comes mostly from Taylor Swift's hit song "We Are Never Getting Back Together."
Cheerful acoustic guitar that's well-known to most people. We expect to hear Swift's voice chime in on the first verse. Instead, Jonathan Davis from Korn jumps in and begins singing "Coming Undone."
The music from "We Are Never..." has been pitch shifted, but by a small enough interval (one half step) that the transposition is imperceptible. The Korn vocals have been transposed by one half step, as well, but in the other direction. The tempo of Davis's singing has also been sped up to match with Swift's guitar part.
Also, as I said in my dissertation, and as Brøvig-Hanssen and Harkins (2012. “Contextual Incongruity and Musical Congruity: The Aesthetics and Humour in Mash-Ups.” Popular Music 31/1, pp. 87–104.) also noted, it's important that the two artists involved in a mashup be from different genres if humor is to result. This track illustrates the principle well. The audiences for the two source tracks are likely to be very different; consequently, it is amusing to find them juxtaposed in a situation like this.
Overall, very solid work by Isosine. Props to Toby King for bringing this to my attention!