Justin Bieber Marvels At Mariah Carey Christmas Collab

Justin Bieber's upcoming Under the Mistletoe album -- you know, the one powered by Christmas cookies and promoted by the first single, "Mistletoe" -- also features more than its fair share of eye-opening collaborations.

That's counting Bieber's mentor Usher (who appears on a version of "Chestnuts Roasting on an Open Fire"), Boyz II Men, the Band Perry and, rather amazingly, Busta Rhymes, who teams up with JB on an updated take of "Little Drummer Boy."

As Bieber told during the live stream that followed the premiere of his "Mistletoe" video, the Busta collaboration is one he'll always remember ... mostly because he considers it to be quite brilliant.

"If you really think about it, it's genius, because it's rapping on a Christmas album ... and, like, I'm rapping on it. And then it's singing," he explained. "It's cool. [Busta's] got, like, a percussive voice to him [and] the beat was so crazy. I'm actually playing drums on that song, playing the snare."

And then, of course, there's his collabo with none other than Mariah Carey, on a version of her instant-classic "All I Want for Christmas Is You." If you thought he was blown away by his Busta team-up, well, you haven't heard anything yet. And he owes it all to none other than Randy Jackson.

"Mariah Carey is doing it with me! It's incredible. So excited," he said of "All I Want." "We wanted Mariah from the beginning, but we kind of thought it was really hard, so we didn't really push the idea. But she's on my label, so we reached out to some people, she got in contact with us, and Randy Jackson was actually at the studio with us, and I was like, 'Yo, you think you can help get Mariah on the Christmas album?' And he was like, 'I'm actually going to see her in New York on Monday,' and I was like 'Yo, go do that!' "

Which Bieber Christmas collabo are you most looking forward to? Let us know in the comments!