WMG / It's Curtains

• But are Mephisto and Beetlejuice cousins?

The Wizard is an Alternate Universe Sweeney Todd.

Specifically, as played by George Hearn in the 1980 filmed version of the stage show.

• Angela Lansbury's Mrs. Lovett was the one who was pulled into Round 0 by the Leading Player, and after the events of Round 1 she moved to Chicago to open up a (hopefully less... humanitarian) pie shop.
• The version of Sweeney Todd who would later become the Wizard was the one left behind. When she was pulled from the timeline, there was no one to cover up his crimes anymore, and he was arrested and hung before he could exact his revenge on the Judge.
• The "dark and vengeful god" he served was none to happy to be robbed of its due, and so this untimely demise awakened the spark of Narrator Magic that's hinted at by Sweeney's fourth-wall breaking lines in the first and last "Ballad of Sweeney Todd." This newly-awakened Narrator Sweeney was able to recognize that his failure stemmed from the Leading Player's decision to pull Mrs. Lovett into her murdergame.
• Due to the bloodlust and the We All Deserve to Die mentality still very much a part of his character, he decides to build power to dismantle the broken timelines by conducting murdergames of his own.
• He included an Alternate Universe version of himself (from the 2012 West End revival) in Round 3, in part to see if there was truly nothing redeemable left inside of him (hence why he erased his alternate self's memories all the way back to before the first Despair Event Horizon, when he was transported for life), and in part to get a glimpse of how he would have turned out, if the timelines had been left the way they should have been.

The path I'm on is paved in blood / I'm cleaning their mess, I did not cause the flood / My home and my family / Is gone, so I'll do what needs done.

• And lastly, why take on the persona of The Wizard? Because George Hearn played him for a short time in Wicked on Broadway, of course!
  • Jossed in the Round 3 endgame, but the Wizard did become who he was because the events of Rounds 0 and 1 screwed up his timeline.

Round 4 will be based on scrapped ideas and proven-wrong theories about 1 through 3.

It wouldn't be It's Curtains without getting ridiculously meta, and they've changed the plot based on theories in the past. Just because the Opera House saga is over and the Cast/Performers have earned a future with no more murdergames doesn't mean it can't be relevant to an Alternate Universe; this might just be set up as an AU in-story as well as out.