This one is a doozy. I admit, I didn’t even know Mizzix’s Mastery even existed before I stumbled upon Darrin Lowe’s decklist.
Basically, the idea here is similar to some of the Mono-Blue Show and Tell decks that we’ve seen throughout Legacy, but instead of trying to back-door an Omniscience onto the battlefield and then cast an Enter the Infinite, this Mizzix Mastery deck seeks to do it from the graveyard.
This deck has some additional strengths and weaknesses. As a benefit, this deck requires one less moving part than traditional Mono-Blue Omni-Tell. The cost is that it is vulnerable to graveyard hate, which can certainly be problematic against the likes of Deathrite Shaman. Darrin has taken some steps to address that by including Izzet Charm as one of his filtering options and even going as far as to include a Pyroclasm that can be found with Personal Tutor.
The sideboard here smartly addresses the graveyard issue. While your opponent may be sideboarding in more hate to interact with you like Rest in Peace, we can simply avoid that issue altogether by transforming into a slightly slower game based around Dream Halls. I imagine that sitting back on Jace, the Mind Sculptor and developing a perfect hand is another great option while your opponent flails around with their mismatched pieces of interaction.
It’s certainly difficult to say that this Mizzix’s Mastery Combo deck is strictly better than Omni-Tell, but that’s a lot of the fun of Legacy. There are tons of powerful things that decks are capable of doing; sometimes we just have to get a little more creative with the execution.