Tyler Posey Credit: Scott Everett White for MTV

The fur is flying! Teen Wolf star Tyler Posey likes to constantly surprise the cast and crew on the set of the MTV drama, which is why he's constantly walking around almost completely naked.

Posey, who plays pack leader Scott, tells Us Weekly exclusively that he recently pulled a prank on set by changing out of his character's clothes and signing out for the day wearing just his underwear.

"I went to go sign out, and I put the pen in my crotch and was holding it with my wiener and signed out with my crotch," the 24-year-old actor admits.

Posey explains that he likes how loose things are for him and his costars, including his close friends Dylan O'Brien (Stiles) and Dylan Sprayberry (Liam).

"I'm always in my underwear, skateboarding, running around," he says. "We goof around every single day. We're, like, bros — we're, like, punk kids."

The second half of the series' fifth season involves the heroes facing off not only against the chimera pack, led by baddie Theo (Cody Christian), but also a new monster known as the Beast.

"The monster's really scary," Posey says, pointing out that the new batch of episodes will involve "lots of death — probably the most death we've ever had on this show."

As for Scott and Kira (Arden Cho)'s romance, Posey promises that there will be plenty of "intimate" moments for the pair.

"[This season] shows them in a different light," he explains. "Now you see the mature aspect of them going through all of this s--t with each other and coming out alive and coming out more mature and as adults. I think it's really fun just to grow their relationship."

Posey points out that he hopes to remain on the show for the duration of its run, and he would even like to serve as its head writer someday if creator Jeff Davis eventually steps down as showrunner, which Davis has hinted at after season 6 wraps up.

"I really want to be the one that takes the show over at the end," he says. "I've heard Jeff talk a lot about leaving. Honestly, I would love that. I really love this show and this environment and this world and MTV, and I think it would be great. I think I would do a good job too — I really care about this show."

Teen Wolf's season 5B premieres on MTV on Tuesday, January 5, at 9 p.m. EST.

Can't get enough of Us? Sign up now for the Us Weekly newsletter packed with the latest celeb news, hot pics, and more!