'Glee's' Grant Gustin Previews Warblers vs. New Directions Michael Jackson Episode (Video)

Slushie Treatment

New Dalton Academy glee club member Sebastian had his sights set on Blaine, but the former Warbler remained loyal to his boyfriend, Kurt, and wouldn't have any of it. The possible result? A slushie.

Who has the right to be "Bad"? That's what New Directions and the Warblers will be facing off over Tuesday when Fox's Glee pays tribute to Michael Jackson with an hour dedicated to songs from the late King of Pop's catalog.

Led by Dalton Academy's newest Warbler Sebastian (Grant Gustin), the dueling glee clubs will go head-to-head when both schools want to perform a Jackson song at Regionals, re-creating the video for "Bad," and covering "Wanna Be Startin' Somethin'," "I Want You Back," "Scream" and "Smooth Criminal."

Gustin tells The Hollywood Reporter that Sebastian will ditch the charming attitude and "take a turn for the mean" as he works hard to ensure the Warblers win the right to feature Jackson.

PHOTOS: 'Glee' Pays Tribute to the King of Pop

"It becomes everyone versus Sebastian," Gustin says. "Everyone turns on him by the end of the episode, including the Warblers."

After rebuffing Sebastian's romantic advances, Blaine (Darren Criss) will become a target for the former flirt, who takes things a bit too far and winds up making an enemy out of Santana (Naya Rivera) in the process.

"Sebastian is more offensive in this episode and I say some things to Santana at the beginning of the episode," he says. "She's pissed at what Sebastian has done to one of her friends -- the slushie to Blaine -- and there's a little extra there and Blaine has to go to the hospital."

STORY: 'Glee': Grant Gustin Poised to be Series Regular

Sebastian and Santana will have their confrontation via Jackson's "Smooth Criminal," a number which Gustin says the duo were allowed to improvise a bit with after choreographer Zach Woodlee gave them a pattern to guide the song. "From there, we got to do what we wanted with the number, it was my most fu n day filming so far," he says.

Elsewhere in the episode, the Warblers will perform their biggest number yet when they cover "I Want You Back," a routine Gustin says features more dancing than the guys have ever done that will take place at Dalton with a pair of New Directions members in attendance. He notes the Warblers aren't trying to lure Blaine back but instead more of a "look how good we are" performance.

Meanwhile, look for Gustin to guest star Sunday on CBS' CSI: Miami 10 p.m., where he'll play twins. As for when he'll return to Glee, the young actor is unsure but optimistic that Sebastian could be back for Regionals.

Watch Criss and company perform "Wanna Be Startin' Somethin' " from Tuesday's Glee Michael Jackson tribute below. 

Email: Lesley.Goldberg@thr.com; Twitter: @Snoodit