Here's a combo for you: Paradoxical Outcome + Vintage. When you tap a Mox Sapphire to play a Paradoxical Outcome and return that Mox Sapphire to your hand, you draw a card, then you get to replay the Mox for free, then you get to tap it for mana again. Essentially, that artifact mana reduces the cost of Outcome by one, and it sticks around to do it again for the next Outcome you draw. If you were to have more artifact mana, the spell would be cheaper, and draw more cards, until eventually you start netting extra mana when you play it. If you were to have a lot of artifact mana ... well ... you would win.
Outcome Combo builds around Paradoxical Outcome with lots of artifact mana, counters to make Outcome resolve, and tutors to chain Outcomes together. Outcome decks are still relatively new to the format, and builds can vary a lot, different players optimizing for speed or resiliency.
Why play Outcome Combo?
Outcome Combo can make big plays at vintage speeds. It's not unheard of for an Outcome deck to draw 30 or 40 cards and generate 100s of storm on the first turn. With enough artifacts in play, Paradoxical Outcome is a strong enough topdeck that an opponent must always be wary of losing next turn, even if the Outcome player has no cards in hand!
Moreso than older vintage combo decks, the core cards of Outcome are almost entirely blue. That makes it easy to run a large number of basic Islands (to defend against Wastelands), and/or painlessly splash an extra color.
Why WOULDN'T you play Outcome Combo?
As strong as Outcome is when you have a board full of mana, it can be a very awkward card when you don't. The mix of lands and artifacts Outcome Combo runs, while explosive, can be unpredictable.
Any "sphere effect" like Thalia, Guardian of Thraben won't stop you from drawing cards, but will make it impossible to generate mana off of replaying artifacts. Leovold, Emissary of Trest can shut down an Outcome entirely.
The Outcome Engine
Outcome Combo decks will run at least 4 Paradoxical Outcome, Black Lotus, Mana Crypt, Mana Vault, Sol Ring, and the five Moxes. To power their Outcomes, decks focusing on speed will run up to 4 Mox Opal. A build more focused on resiliency and consistency might run Trinket Mage. Trinket Mage can find a Mana Crypt or Mana Vault and quickly pay for itself. The next Outcome cast will bounce both and net an extra card and an extra tutor.
Sensei's Divining Top is a useful card to have. Besides just smoothing out draws, an Outcome player can tap a Divining Top to draw a card, and with that ability on the stack, play a Paradoxical Outcome, returning the top to hand. The Outcome resolves first, then the Top's ability, and the Outcome Combo player gets an extra card out of the deal.
The first Outcome isn't as powerful as the second, so it pays to increase the odds of chaining Outcomes together. Outcome Combo decks will run tutors and draw spells to increase the odds of drawing Outcomes back to back.
Some lists run Thoughtcast (usually paired with Seat of the Synod). Others run Thirst for Knowledge, Jace, the Mind Sculptor, or splash black for Vampiric and Demonic Tutor. An Outcome Control might run any, all, or none of these cards.
Snapcaster Mage can be used to flash back a Paradoxical Outcome ... which then returns the Snapcaster to hand ... which then can then flash back another Outcome ...Snapcaster Mage, though you rarely see more than 2 in a deck.
While Paradoxical Outcome can generate a game-ending amount of card advantage, the deck still needs a card to actually kill the opponent.
Some lists splash white to run Monastery Mentor. Outcome decks cast enough noncreature spells, quickly enough, that a Mentor can be lethal the first turn it attacks. Like Tinker, Mentor is a card that can still win a game even if your primary combo plan fails.
Defense and Disruption
As a blue deck trying to resolve a key spell, Outcome Combo runs a mix of counters. 4 Force of Will is a must, and many players run a smaller number of Mental Misstep and Flusterstorm. Some players like to use a pair of Mana Drains, which can act as both disruption and acceleration
Outcome Combo is very vulnerable to lock pieces, so no list is complete without some catch-all removal like Repeal or Chain of Vapor. Anti-Workshop cards like Hurkyl's Recall or By Force are sometimes seen in the maindeck
Outcome decks come in a wide range of builds, from lightning-fast to deliberate and controlling. At this time lists haven't yet coalesced into well-defined subarchetypes.
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