0 - Sacrificing a creature allows us to double our Thaumabrooms
1 - Resolving a contellation trigger allows us to turn many Thaumaturges into sacrifice creatures
2 - Activating Skyway Sniper will put an enchantment into play
3 - Tapping a Forest will generate a bunch of green mana
4 - Casting a creature spell will allow us to put a Forest onto the battlefield many times, thanks to Chulane, Teller of Tales
4 - Activating Steelbane Hydra will allow us to recycle Omen of the Forge, destroying our creature
5 - A Karok Wrangler trigger can put many +1/+1 counters on Steelbane Hydra
6 - Copying an instant can put many Karok Wrangler triggers on the stack
7 - Casting an instant will create many copies
8 - Casting Once and Future will bring the above instant back many times
9 - Tapping a blue painland will generate a lot of blue mana
10 - Resolving a Chandra's Incinerator trigger will gain us a lot of life thanks to Honor Troll
11 - Dealing the opponent damage will trigger many copies of Chandra's Incinerator
12 - A copy of Heliod's Intervention will gain the opponent a lot of life
13 - Casting Heliod's Intervention will create many copies
14 - An artifact can tap for a bunch of white mana
15 - Casting Mythos of Nethroi will create many copies of our artifact
16 - Tapping Skull Prophet will generate a lot of black mana
17 - A copy of Lorehold Command can give a lot of Skull Prophets haste
18 - Casting Lorehold Command will create a lot of copies
19 - Casting Tibalt's Trickery will allow us to cast Lorehold Command many times
20 - We can put many copies of spells below the initial Tibalt's Trickery
21 - Tapping a snow land will generate a bunch of red mana
22 - Attacking with Jorn, God of Winter untaps a lot of snow lands
23 - We can attack with many Jorns each combat phase
24 - We can get a lot of combat phases thanks to Moraug, Fury of Akoum
Unfortunately, to make this work, we need an artifact that can tap for white mana, but not black or red mana. (what a concept ) So here's hoping that more mana artifacts will come out. Another possibility is to use Zagoth Crystal to transition to black mana, and then have a creature tap for white mana - but we don't currently have a creature that taps for white mana but not red mana.
Keep on running into random holes in the stage frameworks I'm trying to find.
For example, Rewind is kinda similar to devious cover-up if you squint but only if we have a good come into play tapped land that sacrifices, oh we got a whole cycle of them, nice... But they can mostly only be activated at sorcery speed and the instant speed ones don't give us anything that the thaumabroom combo wouldn't do better.
Hmmm... for a stage, we don't need to necessarily do better than the thaumabroom combo, and we don't have to have the thaumabroom combo in the deck. (Although admittedly the combo is convenient for certain things)
What about Gates of Istfell? Its nonmana ability costs two blue, the same as Rewind, and gaining two life an drawing two cards could potentially be useful.
Edit: Actually, I think that can work. Let's say we have an easy way to recycle lands with draws - say we have a sacrifice outlet, and a way to put land cards from our graveyard into our library. If we have some Rewinds on the stack, and some number of Gates of Istfell, and a couple of blue mana lands that come into play tapped, we can resolve a Rewind to untap the two blue mana lands and a Gates of Istfell. We can get two blue mana from the lands. Then we sacrifice the two blue mana lands, and put those two lands along with a Gates of Istfell into the library. We sacrifice the Gates of Istfell (let's say we can get white mana on the cheap), and draw 4+ cards thanks to Teferi's Ageless Insight, including the two blue mana lands and a Gates of Istfell. We have some cheap way of putting those lands into play, and we profit some life. We do this for each Rewind on the stack, until we get to a Rewind followed by a Gates of Istfell activation below it. So now we can resolve the Rewind and Gates of Istfell without needing to spend any blue mana, so we profit two blue mana. We then resolve the next Rewind on the next layer below, so that we can untap a Gates of Istfell and two blue mana lands (so we go up to sfour mana), and spend two of our newly acquired two blue mana to activate the Gates of Istfell, but we don't resolve it. Then we cast Rewind with our remaining two blue mana, and get lots of copies, so we our back to where we started, except with a new top layer (presumably larger due to more copies... I guess we will have to make more copies of Sea Gate Stormcaller, and precast Teach By Example prior to casting the Rewind), and the next layer down being one copy less. So, this looks like a stage? Barring the rest of the setup, of course.
Hmm, that's kinda close, but runs into some problems like the Rewinds running out of targets, (all of the copy triggers only make one spell at a time) and gates of istfell being only one activation instead of several.
Then we need the other spell to put the Gates of Istfell back into play (gates can draw itself) Eureka moment can do that, but costs UG instead of UU...
I guess U=G isn't obviously a big problem, and we still need to turn the 2 life into the proper mana. Something like Murderous Rider can kill Maraleaf pixie for 2 life, allowing the pixie to be brought back with Back for more, though that does add another green to the cost...
We also have to be careful about consequences of reusing the Tibalt's trickery from the setup.