The Arrowverse will experience its latest crossover event this week when the Music Meister (Darren Criss) places both Supergirl and The Flash under his spell, whisking them away to an alternate reality where in order to escape they'll need to live out his 1940s musical fantasy. On the surface, it's just another wacky villain come to play havoc with our heroes, but behind-the-scenes it's an excuse to have the more musically-inclined Arrowverse stars sing and dance -- and we aren't complaining!

But just who is the Music Meister, and how can he force these powerful superheroes to do his bidding? To answer that, we need to take a closer look at the Music Meister's first and only other appearance in a DC Comics property -- the animated series, Batman: The Brave and the Bold.

Created by James Tucker and Michael Jelenic, Batman: The Brave and the Bold was a quirky take on the typical Batman cartoon formula, with a tone and style closer to that of the campy 1960s Batman TV series. And being that it was such a oddball show, including an episode in which Batman and his allies are menaced by a musical villain -- with both heroes and villains alike being forced to sing their hearts out -- didn't seem that strange at all.

Mayhem of the Music Meister

Music Meister from Batman the Brave and the Bold

It's in the season 1 episode of Batman: The Brave and the Bold, 'Mayhem of the Music Meister' -- written by Michael Jelenic and directed by Ben Jones -- that the musical menace makes his debut. Voiced by Neil Patrick Harris, the Music Meister comes to Gotham in order to steal a satellite that is capable of broadcasting his hypnotic voice all across the globe. Doing so will allow him to place the entire planet under his trance and achieve total world domination. Just regular, maniacal villain stuff. It's then up to Batman and Black Canary to stop him, and the two vigilantes get caught up in the singing spectacle along the way.

What makes 'Mayhem of the Music Meister' such an entertaining episode is its songs, which both poke fun at much of the Batman mythos and explain the Music Meister's origin and powers. Bullied at school for singing in the choir as a child, the Music Meister -- whose alter ego is never revealed -- discovers that when he sings in a high pitch he can place anyone in earshot under a hypnotic spell. Those affected by the Music Meister's powers are then compelled to break out in song and dance in addition to obeying his every command. He then grows up to abuse that power, becoming a supervillain who places others under his control and makes them do his evil bidding.

Batman, of course, manages to avoid being hypnotized by using ear plugs, dampening the mind control effects of the Music Meister's powers. In their final battle with the Music Meister, after he has the entire world -- including heroes like Green Arrow and Aquaman -- under his control, Black Canary's ear plugs are removed and she too comes under Music Meister's control. It's then that Batman, clever as ever, tricks the Music Meister into making Black Canary sing at a higher and higher pitch until she triggers her Canary Cry, cancelling out the Music Meister's hypnotic spell.

The Arrowverse's Music Meister

Flash Supergirl Crossover Duet Kara Barry Music Meister

Judging by what's already been shared about 'Duet' and what we can learn from the Music Meister's quick appearance at the end of tonight's Supergirl episode, the Arrowverse's version of the Music Meister won't be exactly like the villain from Batman: The Brave and the Bold. For starters, it doesn't appear as if his mind control works from singing but rather from staring into the eyes of his victim (visually represented by what looks like sound waves pulsing across the eyes). And it isn't really mind control either, at least not in the way that Brave and The Bold's Music Meister used it.

What we see during the final minutes of 'Starcrossed' is the Music Meister look at Supergirl, transfixing her with his gaze. Their eyes pulse in the same rhythm and she tosses him the inter-dimensional extrapolator, which he uses to open a portal to The Flash's Earth and escape. Kara then collapses, either in some kind of deep sleep or coma, but either way she "awakens" in another world -- backstage at a music club circa the 1940s.

What follows will have to wait for 'Duet', but we do know that J'onn 'Jonzz and Mon-El bring an unconscious Kara to Star Labs looking for help. But before they can do anything, the Music Meister appears and places Barry in a similar coma, trapping him in the same alternate musical dimension as Kara. While inside this 1940s pocket universe, Barry and Kara will cross paths with alternate versions of Iris, Joe, Cisco, Mon-El, and Wynn as well as Martin Stein and Malcolm Merlyn. They'll all be singing and dancing and just generally indulging in their musical sides (not to mention enjoying a a Glee-reunion between Grant Gustin, Melissa Benoist, and Darren Criss).

It's still not clear for what purpose the Music Meister traps Supergirl and The Flash or why he's making them perform, but it clear that if they don't follow his script, he'll never let them leave. Also, as another tiny stipulation, if they die in this musical world, they die in the real world. So Kara and Barry better steer clear of gangsters and any other shady people because they don't have their powers in the musical world. Just their singing voices and tapping feet.

Next: Mon-El’s Royal Past Explained

The Flash/Supergirl crossover episode 'Duet' airs Tuesday night @8pm on The CW.