I saw a reddit post and built my list off it:
So, for the uninitiated, there is actually a
Doomsday-like combo in this deck. Before that though, the basic plan is to get to 4 mana, then cast
Irencrag Feat +
Goblin Charbelcher to win. There are no lands, so Belcher does damage equal to your library size. With a single ritual, this can happen on turn 3. I view it as an A+B combo, like
Ad Nauseam or
our boi on the banned list, so I have 4 copies of both, even though Irencrag Feat is clearly useless in multiples. Also notice both pieces are immune to
Inquisition of Kozilek.
Without Feat, you can cast and activate Belcher (4+3 mana) over 2 turns. With a single ritual and untapped land drop on turn 3, Belcher lands T3 and activates T4. Or, you can ritual all the way up to 7 mana and do it in 1 turn. This is less common because the rituals only give a net +1 mana, unless it's a spliced
Desperate Ritual, and
Wild Cantor only lets you store 1 mana at a time (compared to my previous Belcher deck's
Vessel of Volatility).
Now, the Doomsday combo. This deck's Doomsday equivalent is
Recross the Paths. Get to 2G, then cast Recross the Paths, reveal your land-less library, and rearrange it this way: set aside one Turntimber, one
Reforge the Soul, at least 2 SSGs or SSG+untapped land, any 2 rituals, Feat, Belcher, and any other card you think will help. Pact won't, because Feat restricts you to just the Belcher after it. Then put those on top of your library, making sure Turntimber is on top and Reforge is below it. Clash and probably win, returning Recross to hand and bottoming Turntimber. On your next turn, draw and miracle the Reforge, drawing into your rituals and Belcher, cast everything and win.
Remember that you need 2 mana the turn after you Recross to cast Reforge. If you only have 1 land, no Cantors in play and manage to generate 3 mana for Recross, you're not clear yet: you still need an extra SSG in hand to Reforge next turn. Given that you probably also used an SSG for Recross, and the Reforge pile needs 2 SSGs in it, that's all 4 SSGs right there. If, on the other hand, you have 3 or more lands, then you can cut rituals from the Reforge pile.
Instead of Feat in the pile, you can have two more Desperate Rituals instead, providing the same net +3, but over two cards instead of one. If you have 3 lands, this lets you put Pact in the Reforge pile for protection.
Pact and Reforge are at 2 to reduce the risk of getting shafted from drawing them naturally before Recrossing. Note that Reforge makes you discard, so you can't save those if you draw them naturally. For the same reason, don't use
Chromatic Star while making mana for Reforge. If you only have 2 green lands then that can't be helped, but this just means you have to put one junk card below Reforge, above its pile, that will be discarded to it.
The 7 cards below Reforge can be further arranged in a way that maximizes your chances for recovery if Reforge is countered. While deciding on the Reforge pile, look at your hand and field and figure out what you're missing from either the Feat+Belcher combo or another Recross cast, and put that directly below Reforge. Since you almost always win the clash and need 2 lands to cast Reforge, the easiest option is to just put SSG right below Reforge, so if it's countered, next turn you'll draw SSG and can Recross again. However, if you're only 1 card away from Feat+Belcher, e.g. 3 lands and ritual+Belcher in hand, you can save a turn over Recross by putting the missing card (in this case Feat) below Reforge.
Alternatively, if you're only 1 card away from Feat+Belcher, you can put Turntimber on top, the missing card below that, then Reforge and the pile (so you go for Feat+Belcher first, then Reforge if that fails, instead of the other way around). If you have Manamorphoses in hand or Stars on the field, you can put that many other missing pieces below Turntimber.
Against slow decks with counterspells, if you aren't in danger of dying within 2 turns, you don't need to set up a Reforge pile that wins next turn. Reforge gives them a new 7 too, and if they have Force + blue card + another counterspell, they can beat your 1 Pact/Veil. Suppose it's a postboard game, you have 3 lands in play, and resolve Recross. If you set up the Reforge pile as SSG, rit, rit, Desp, Desp, Belcher, Pact, attempting to win next turn, you have 1 piece of protection for them to try to beat. If instead you go land, Veil, Pact, Pact, Feat, Belcher, Turntimber/Shatterskull (depending on whether you need R for Feat or G for Veil), you kill 1 turn later, but have 3 pieces of protection. (Once Feat resolves you can't Pact, but you just need to protect Veil. If they have
Aether Gust and try to use it on Feat you can still Pact those.) This is made possible by waiting for your lands to untap after spending 2 of them on Reforge, allowing you to cut rits for protection.
If you're out of Reforges in your library but have 4 lands, you can stack Feat, Belcher, Feat, Belcher... repeatedly, attempting to combo off every other turn. This works against decks that have removal to stop a slow 2-turn Belch. Against decks with discard or counterspells, you can stack all your Belchers, then all your Bala Ged Recoveries. If you have fewer than 4 lands in hand and field combined, just stack as many as you need on top of the wincons.
The Chromatic Stars in the main are there for fixing Pyretic/Desperate Ritual mana for Recross usage. I like those better than
Mishra's Bauble or
Street Wraith because they actually do something while cantripping. DS uses those cards to feed
Gurmag Angler or
Death's Shadow. This deck has no such excuse, but instead has cards that generate RRR and another card that costs 2G. Postboard they come out and whichever 4 cards you need most against your opponent come in. Leyline for discard, Claim for
Stony Silence, Veil for counterspells, Anger/Slash for creatures. Pacts come out instead if your opponent has no counterspells. The A+B combo angle is weak against decks with discard or counterspells, so 2 Feats can be cut in that case.
Mana wise, the on-color ETB untapped bolt lands are obviously at 4 each, then I have 8 more red sources and 4 green. These are mainly chosen by how much utility their nonland sides provide: Spikefield Hazard can ping a hatebear, Valakut Awakening lets you mulligan, Bala Ged Recovery gets back a combo piece. They could be Tangled Florahedrons instead if you think they'll help in hitting 7 mana for one-turn Belches, but the
Recollect is probably better. Don't drop to 16 red/4 green thinking only 1 card uses green anyway and you should be fine with all your fixing, you need green sources postboard since you bring out Stars and bring in green spells.
This deck can win on turn 1 if you draw the Reforge pile as your opener. You can win turn 2 with a T1 Recross, but the hand is very specific: untapped land (/8), 2 SSGs (/4), ritual (/8), Cantor (/4), Recross (/4), any non-SSG wildcard OR another ritual+Star instead of Cantor+wildcard, and you mustn't draw SSG off it.
Recross is amazingly weak to
Field of Ruin, since the (failed) search and subsequent shuffle (messing up library order) are forced, and the deck has 0 basics.
Assassin's Trophy is optional, so choose not to search. If you have Manamorphose or Star with floating mana, you can save the top card at least.
Final tip is that you can use Irencrag Feat to cast Shatterskull Smashing for X=5, or for 1 more mana, basically kill 2 things. This answers
Karn, the Great Creator. I wish there was something we could do with Turntimber Symbiosis, but there isn't.