Back in 2012, Jimmy Fallon and The Roots sang "Call Me Maybe" with Carly Rae Jepsen and it was the greatest thing ever. Months later, though, it got even better. Fallon and the band were joined by Mariah Carey on what was then Late Night With Jimmy Fallon, and they cranked out a rousing rendition of her holiday pop classic, "All I Want For Christmas Is You." Though Carey's recorded version will indubitably be played millions of times in the coming weeks, you probably won't hear anything like this. Fallon and company are playing their toy instruments and a small chorus of kids are on backup, while everyone is dressed in their holiday finest. It's totally irresistible, even for the most Grinch-like viewer.