Justin Timberlake may have been billed as the musical guest on "Saturday Night Live" tonight (Dec. 21), but for all intents and purposes, think of him as a backup host of sorts. 
 
 For the show's final episode before Christmas, the singer and actor appeared alongside host Jimmy Fallon as a veritable dream tag team for the show, guesting in a number of sketches in addition to his performing duties. All this was stacked between a score of cameos from musicians, actors and politicians alike. The tagline for this episode? "Why not?" 
 
 Though he basically took on a role as second host, Timberlake was there to sing as well, performing two cuts from "The 20/20 Experience -- Part 2 of 2." Rather than start with one of the album's main singles -- such as "Take Back the Night" or "TKO" -- the former boybander went deep in the tracklist for "Only When I Walk Away." The performance itself had a sort-of Kanye-esque vibe to it, with more lasers than a Trans-Siberian Orchestra show. His vocal was clothed in distortion, own head floating on screens behind him as he danced around the stage, acting as puppetmaster with the light spectacle on occasion, the lasers dropping in sync with his hand movements. 
 
 For performance No. 2, he retreated to the other side of the spectrum, shedding the busy set for yet another number from the tail end of "The 20/20 Experience"'s second part: "Pair of Wings," a hidden track on the album stuck after "Not a Bad Thing." Armed with an acoustic guitar and backed by a few guitarists and a tiny orchestra of strings, Timberlake crooned the soft-spoken, subdued ballad, providing a fairly beautiful end to the show that could have viewers revisiting his latest album; he certainly repped its ending. 
 
 It's become a staple of any Justin Timberlake "SNL" gig to revitalize his overly enthusiastic salesperson character who works for an assorted amount of establishments ending in the suffix -ville. This year, it was Wrappinville, just in time for the holidays. Joined by Fallon, the duo advertised the joys of the perfect wrap job on one's present, set to music from Ludacris, Macklemore, 2 Live Crew and Gotye ("Now you're just a present that I used to know"). 
 
 Was that it? Naturally, nah. In one of the evening's funnier moments, Timberlake portrayed Fallon himself on "Family Feud: Celebrity Edition," overemphasizing the late night host's mannerisms -- mostly his movements -- to a T, causing Fallon to cower behind his podium, unable to control his laughter (which, of course, is a classic tenet of a Fallon "SNL" appearance). 
 
 Then came the indomitable "Barry Gibb Talk Show" sketch, again a recurring aspect of nearly any Fallon/Timberlake show, this time featuring Madonna -- playing herself -- seducing Fallon's Barry Gibb ("She's tamed me like a wild horse"). But the cameos weren't done, as Barry Gibb himself walked out at sketch's end to harmonize with, you know, himself. 
 
 In addition to Timberlake's acting pursuits, the show gave Paul McCartney a quick guest role in Fallon's monologue as the duo serenaded audiences with "Joy to the World" and "Have Yourself a Merry Little Christmas," the latter including a light snowfall inside 30 Rock. 
 
 The show also brought back its "Waking Up With Kimye" sketch, lampooning Kanye and Kim's "Bound 2" video for the holidays. "Uh huh, Rudolph," purred Nasim Pedrad's Kardashian while the power couple straddled a reindeer. 
 
 Naturally, a Fallon episode wouldn't be anything without a chance to break out a number of impressions, either. In a sketch advertising a new NOW Christmas compilation, the former "SNL" cast member did his best Michael Buble and Harry Styles, the latter basically involving him standing in the background and giving the spotlight to Lorde before adding in a sporadic jump for good measure. 
 
 It was also Seth Meyers' last episode as a cast member, getting a proper sendoff on Weekend Update by Fallon, who he'll replace on "Late Night." 
 
 "SNL" returns Jan. 18 with a host-and-musical-guest combo from Drake. 

 Last night's very special Christmas episode of SNL would've been exciting just for its billed guest appearances -- former cast member Jimmy Fallon returned to his old seat at the Weekend Update desk, and Justin Timberlake appeared throughout the nights in skits and as the musical guest. 
 
 Then things got really crazy, with celebrity "guests" more than once turning out in the flesh to up-stage the cast's usual impersonations. 
 
 Fallon performed a musical opening monologue along with David Bowie, Bob Dylan and the actual Sir Paul McCartney -- the last one who showed up mid-way through Fallon's aborted Dylan impression to join the host in a rendition of "Have Yourself a Merry Little Christmas": 
 
 One of the night's recurring sketches, the "Barry Gib Talk Show," this time featured the Bee Gee himself, and featured appearances by Megyn Kelly, Paul Ryan and the (real) Madonna, who shared some ideas for fixing our broken political system: 
 
 And finally, New York City Mayor Michael Bloomberg dropped by Weekend Update to chat future plans ("fulfilling a lifelong dream of drinking a small soda on a non-smoking beach"), thus fulfilling a storied tradition:
– Saturday Night Live had itself a merry little star-studded Christmas episode last night, with SNL alum Jimmy Fallon guest hosting, while Justin Timberlake played musical guest ... though as Kevin Rutherford at Billboard notes, "for all intents and purposes, think of him as a backup host of sorts." The duo went to town, with Timberlake impersonating Fallon on "Family Feud: Celebrity Edition," before combining on "The Barry Gibb Talk Show"—where none other than Barry Gibb joined in a surprise cameo, along with Madonna. And the cameos did not stop there, notes Lindsay Abram at Salon: "Things got really crazy," with appearances by Paul McCartney, Michael Bloomberg, Megyn Kelly, and Paul Ryan. Check out highlights in the gallery.