At the risk of DJ-splaining, a medley is a varied mixture of people or things; a miscellany, like a bag of frozen mixed vegetables or a 4 AM tavern. (Remember those?)
To mash up is to mix or combine two or more different elements, like a bag of miscellaneous meat parts and a bag of frozen Asian style vegetables. In this case, by definition, the following qualifies as both a medley and a mash up.
Oddly, this mash up came to me in a dream. Let it be known, I am not a fan of post-Derek & The Dominos Eric Clapton, yet I dreamt that I had made a mash up using my least favorite song, “Tears In Heaven”. All I think about is the joke: What’s the difference between Eric Clapton’s son and a bag of cocaine? Eric Clapton wouldn’t let a bag of cocaine fall out the window.
And for good measure: What does Eric Clapton have in common with a cup of coffee? They both suck without cream.