“Doctor Who” will air its 10th annual Christmas episode Christmas Day. A landmark anniversary calls for a big celebration, and it doesn’t get any bigger than Santa Claus himself. Guest star Nick Frost will play the man in red. Fans first got a sneak peek of him in the Season 8 finale. The Christmas special will show the Doctor (Peter Capaldi) at the North Pole with St. Nick. While we aren’t entirely sure why the Doctor hasn’t met Santa before, we do know a few things about the episode.

1. Rudolph appears -- What’s Santa without his red-nosed reindeer? A sneak peek video shows Santa’s entrance on Rudolph. It also seems that Santa’s elves are bodyguards. Watch the sneak peek video below:

2. He’s a funny Santa -- Frost makes his Santa a little different than a jolly old elf with a cookie addiction. “There’s a percentage of ‘ho, ho, ho’ as every good Santa needs, but that’s all people ever see of Santa,” Frost explained in a press release. “They never see him day-to-day or when he’s a bit grumpy, or when he’s in a playful mood or if he’s a bit cross. I’ve tried to get all those sides to him. Hopefully he’s funny. I wanted him to be funny, and I wanted him to be like what he is essentially -- and that’s the spirit of Christmas.”

3. Tangerines -- Tiny orange fruit plays a big part in the “Doctor Who” Christmas episode, but no one knows why. Yes, that does sound weird, but we don’t think the promotional team just added the fruit to the photos for kicks. They’ll somehow play a part in the episode.

4. It’s a dark episode -- While visiting the North Pole may seem like a silly, campy idea, it also seems like the episode will be a scary one. “It makes you question reality,” actress Jenna Coleman, who plays Clara on the series, teased to BBC. “You can’t quite figure it out. It makes you question what is real and what isn’t, but with a thriller and psychological element. It’s very 'Doctor Who' -- it’s got all of the traditional elements as well, and the one sequence we have with the sleigh is so magical.”

The episode will be especially dark when a mysterious message appears on Clara’s classroom chalk board that says, “You are dying.” Check out the message in the promo video below:

5. Clara might leave -- While Coleman won’t say if “Last Christmas” is her last episode, the title has made many fans suspicious. The actress recently revealed she spoke to showrunner Steven Moffat about keeping details of her character's fate sealed. “Because there’s a surprise we’ve got coming, it’s much better that nobody knows which way it’s going to go -- so that’s where we’re trying to keep it at the moment,” she told Radio Times in the fall.

6. It will focus on relationships -- Whether she’s leaving or staying, the episode will focus on Clara’s relationship with the Doctor. “They’re brought together by a crisis that returns the Doctor to Earth to help Clara,” Moffat explained in a press release. “The stuff that separated them, the lies they told each other -- all of that will be addressed in this episode.”

The "Doctor Who" 2014 Christmas special airs Thursday, Dec. 25, at 9 p.m. EST on BBC America. Do you think Clara is leaving? Sound off in the comments section below!