Sorcery tribal with Umori.

Main combo is:

• Tutor for Boundless Realms or play a bunch of ramp cards
• Use Regrowth or Regrowth adjacent cards to play Boundless Realms or other ramp cards again.
• Control the board with board wipes, lots of zombies, and playing Umori over and over again when it dies
• Stall long enough to tutor for Skull Storm and Twinning Staff, or just draw into it (there's a lot of draw)
• Play Twinning Staff and Skull Storm in that order, copying it X+1 times with Skull Storm's first ability (hopefully you have been casting your commander)
• Use twinning staff's ability to copy it 2 more times.
• Next turn, use recursion or Sins of the Past to do it again.

That's the main line because Skull Storm is really hard to get around, especially with how many board wipes we have. Hope your opponent doesn't run Mindbreak Trap.
Here's a helpful rule to calculate how many Skull Storms you need to kill your opponent. And yes, you CAN kill your opponent exclusively with Skull Storm, because half of 1 is 0.5 and 0.5 rounded up is 1, meaning they lose their last life point. Plenty of people misunderstand that, so I thought I would mention it.

Remember to add a SS for each creature they have!

Of course, you could just cast huge spells over and over instead! I always found Exsanguinate less fun than 20 skull storms, but to each their own.

P.S: Yes, I run Seedtime in the 99. Yes, I have played games where none of my opponents even have blue in their deck, but it kind of rules.

>OLD DESC:

Sorcery Tribal. Simple as.

Lots of pet cards and niche removal here for my playgroup. If you want to build something like this, probably build it from scratch. And message me your list! YMMV with this deck.

There's a few wincons, and lots of tutors/draw.
Praetor's Counsel + Neverending Torment can usually remove a player from the game each turn. (Even better when copied!)
Choice of Damnations or Skull Storm or Curse of the Cabal can be recurred and cast again and again.
Command the Dreadhorde, Breach the Multiverse, and a bunch of other recursion can make up for not having creatures. Board wipes can keep you alive until you reach that point.
And of course, you can copy all of this with Mirari or Twinning Staff or Lithoform Engine.