Heads up, because this weekend's Saturday Night Live is about to be epic. The holiday episode has host Jimmy Fallon plus musical guest Justin Timberlake, and Fallon's promos are hilarious to boot. JT may not appear, but that doesn't stop Fallon from singing "Mirrors" — a ridiculous, mumbled version with Kenan Thompson anyway — and he also whips out his own guitar and breaks it down with Kate McKinnon. Seriously, there are so many funny parts to this promo, I can't pick a favorite (and make sure you watch until the very end!).