Supergirl is set to join forces with The Flash once more, when both shows combine in a special musical crossover episode. "Duet" will see Melissa Benoist's Kara and Grant Gustin's Barry teaming up to follow the script set by the villainous Music Meister, in order to escape the alternate reality that he's trapped them in.

The episode serves as a Glee-union of sorts, since former Glee Warbler Darren Criss takes on the role of the Music Meister, having previously starred opposite Benoist and Gustin on the musical show. Various trailers and promotional images have surfaced ahead of the highly anticipated episode, and now a new clip has arrived, showing Criss making his debut as the Music Meister on tonight's episode of Supergirl. Take a look, above.

A suave, sophisticated villain with a penchant for music, Music Meister sounds pretty perfect, apart from the whole villainous side to him. Clearly, Kara is under his powers right away, so does she willingly follow him into the new dimension he opens up in the clip? Presumably this video is from the end of the episode "Star-Crossed", which will then lead into the crossover "Duet" (which airs tomorrow, March 21st).

Either way, Kara and Barry end up trapped, and the hypnotic Music Meister has them under his evil spell. However, the all-singing, all-dancing villain hasn't reckoned on coming up against Barry and Kara's friends, Kid Flash (Keiynan Lonsdale), Vibe (Carlos Valdes), and Martian Manhunter (David Harewood). Though they might be outside the alternate reality, in Central City, they will still face off against the Music Meister and hold him to account.

Confirmed to be singing in the episode alongside Gustin, Benoist, and Criss, are Cisco Ramon/Vibe, Joe West (Jesse L. Martin), Professor Martin Stein (Victor Garber), Winn Schott (Jeremy Jordan), and Malcolm Merlyn (John Barrowman), and for fans of musical theater, it's almost too exciting to contemplate. That doesn't mean the episode will be for everyone, though. It's a tricky mash-up; two superhero TV shows coming together in an alternate reality where there's singing, dancing, glitzy costumes, and original songs to boot. It remains to be seen whether The CW can pull this off or not, and if it is well-received, whether it could lead to more Arrowverse musical opportunities in the future.

NEXT: Arrowverse Crossovers to Continue Yearly

Supergirl continues with ‘Star-Crossed’ on Monday, March 20 at 8 p.m. EST, followed by The Flash on Tuesday, March 21 in the same time slot with ‘Duet’.

Source: ET Tonight