Enter Splinter Twin.
Anyone who has talked to me about modern knows my answer to the question: “what deck should I play this weekend?”. Choosing to play anything but a Splinter Twin deck in modern just seems insane to me unless you can very accurately predict what the field of a tournament will look like, and even then, there is a good chance Splinter Twin is still just the best choice. The main draw of Twin decks is the fact that they are generally well-situated to interact with faster, more linear decks with cards like Remand, Spell Snare, Lightning Bolt, and Dispel while having a way to instantly win the game before your advantage is lost. The reason Twin has been tier 1 for as long as it has is for this very reason: faster combo decks exist, but Twin can stop them from winning for as long as it takes to set up its combo to close the door. If you aren't playing Splinter Twin or another instant-win combo in your Lightning Bolt/Remand/Snapcaster Mage deck, the time you buy against a linear deck with these cards does not matter as much, as they will have many more turns to make attempts at doing whatever powerful thing they are trying to do to beat you.U/R Twin by Sam Pardee
4 Deceiver Exarch
2 Pestermite
4 Snapcaster Mage
1 Vendilion Clique
4 Splinter Twin
2 Cryptic Command
2 Dispel
2 Electrolyze
4 Lightning Bolt
1 Peek
4 Remand
1 Spell Pierce
1 Spell Snare
1 Roast
4 Serum Visions
4 Island
1 Mountain
1 Cavern of Souls
2 Desolate Lighthouse
4 Misty Rainforest
4 Scalding Tarn
3 Steam Vents
1 Stomping Ground
3 Sulfur Falls
Sideboard:
1 Spellskite
1 Grim Lavamancer
2 Blood Moon
2 Ancient Grudge
1 Negate
1 Rending Volley
1 Teferi, Mage of Zhalfir
2 Keranos, God of Storms
1 Jace, Architect of Thought
2 Anger of the Gods
1 Roast
The current U/R builds of Splinter Twin have a few notable advantages over the three-color versions. The first, and I believe the most important advantage these builds have is the near-perfect mana. Playing U/R, you will rarely have to take many points of damage from your lands, and you are not very susceptible to common manabase-hate like Blood Moon, Spreading Seas, and Tectonic Edge. Some U/R Twin decks even mainboard Blood Moon at little cost, and I've played versions with 2 Tectonic Edges maindeck without having any colored mana issues at all. Not having to worry about your colored mana situation certainly beats the feeling of playing a three-color version of Twin and having both Cryptic Command and Kiki-Jiki in your hand, while being able to cast neither. Another slight edge the U/R builds have is the option to devote more slots to finding the combo, protecting the combo, and the combo itself. There are matchups and metagames where comboing or casting Blood Moon is Plan A, and in those cases I think U/R is the best option.
RUG Twin by Patrick Dickmann
3 Deceiver Exarch
2 Pestermite
4 Snapcaster Mage
4 Tarmogoyf
1 Vendilion Clique
3 Splinter Twin
2 Cryptic Command
1 Dismember
1 Dispel
1 Electrolyze
4 Lightning Bolt
4 Remand
1 Spell Snare
2 Gitaxian Probe
1 Roast
4 Serum Visions
1 Forest
3 Island
1 Mountain
1 Breeding Pool
1 Ghost Quarter
1 Hinterland Harbor
4 Misty Rainforest
4 Scalding Tarn
2 Steam Vents
1 Stomping Ground
3 Sulfur Falls
Sideboard:
1 Spellskite
1 Izzet Staticaster
2 Thragtusk
2 Ancient Grudge
1 Counterflux
1 Dispel
1 Nature's Claim
1 Negate
1 Keranos, God of Storms
2 Pyroclasm
1 Roast
1 Desolate Lighthouse
RUG Twin surfaced last year as a response to a Splinter Twin and Birthing Pod-heavy metagame. Tarmogoyf is excellent in the mirror as the U/R decks don't pack very many ways to deal with one once resolved. RUG Twin should be thought of mostly as a tempo deck that has the Splinter Twin combo in it to hedge against fast, linear strategies and to force its interactive opponents to make plays they normally wouldn't if they didn't have to worry about getting combo-killed. I've noticed when playing RUG Twin that some percentage of the time players will spend removal spells on Pestermites and Deceiver Exarchs or pass their turn without using their mana when an unanswered 4/5 Tarmogoyf is beating them to death. Sometimes your opponent's fear of the combo is more powerful than the combo itself.
The green also gives you some nice sideboard options for grindy matchups like Huntmaster of the Fells and Thragtusk, and also gives a little bit more flexibility with what hate cards you can run. I'm not sure if the current metagame is one where RUG Twin is a deck I would choose to play however; the deck is still weak to Abrupt Decay, and with a big resurgence in the number of fast ultra-linear decks such as Amulet/Bloom and Goryo's Vengeance, I'd rather not be casting vanilla green creatures. That being said, this deck has certainly shown that it has its time and place, even if that time and place is not right here, right now.
Grixis Twin by Dylan Donegan
4 Deceiver Exarch
2 Pestermite
4 Snapcaster Mage
3 Tasigur, the Golden Fang
3 Splinter Twin
2 Cryptic Command
3 Kolaghan's Command
4 Lightning Bolt
4 Remand
2 Spell Snare
2 Terminate
4 Serum Visions
4 Island
1 Mountain
1 Swamp
1 Blood Crypt
1 Bloodstained Mire
1 Desolate Lighthouse
4 Polluted Delta
4 Scalding Tarn
2 Steam Vents
2 Sulfur Falls
1 Tectonic Edge
1 Watery Grave
Sideboard:
1 Spellskite
2 Blood Moon
1 Splinter Twin
2 Dispel
1 Negate
1 Olivia Voldaren
1 Vendilion Clique
2 Keranos, God of Storms
2 Anger of the Gods
2 Shatterstorm
There was a time a while ago where people were trying to play Grixis Splinter Twin decks in modern, splashing black for discard spells and better removal spells like Terminate and Go for the Throat. Those decks never really put up good numbers, but Khans of Tarkir block has presented some interesting and powerful options for Grixis Twin decks going forward. Tasigur, the Golden Fang is exactly the threat that Twin decks have been looking for to justify a black splash. A 4/5 for one, two, or even three mana is a rate that is hard to turn down, and his activated ability gives Twin decks another way to grind out card advantage. Tasigur is certainly very good, but Kolaghan's Command is to me what really solidifies Grixis Twin as having a valid place in the modern metagame. There are spots where it is slightly worse than Electrolyze, but the number of times where it is far better than Electrolyze could ever hope to be justify running it instead.
Which build of Grixis Twin is the best one is as of yet undetermined. Some builds focus more on getting Tasigur into play quickly with cards like Thought Scour. Some builds run more discard spells and focus more on comboing. Some builds look like a U/R deck splashing Kolaghan's Command, Terminate and a few black sideboard cards. Some of the lists are built to play Blood Moon in the sideboard, and some lists have manabases that look like they straight lose to the card. I'm sure there is validity to each of these, but if I were to play Grixis Twin in a tournament tomorrow, it would probably look like this,
Nate's Choice
4 Deceiver Exarch2 Pestermite
2 Tasigur, the Golden Fang
4 Snapcaster Mage
1 Vendilion Clique
4 Serum Visions
4 Lightning Bolt
1 Dispel
1 Spell Snare
4 Remand
2 Kolaghan's Command
2 Terminate
4 Splinter Twin
2 Cryptic Command
4 Scalding Tarn
4 Polluted Delta
1 Bloodstained Mire
2 Steam Vents
1 Blood Crypt
1 Watery Grave
2 Sulfur Falls
1 Cascade Bluffs
1 Desolate Lighthouse
4 Island
1 Swamp
1 Mountain
Sideboard:
1 Keranos, God of Storms
1 Wurmcoil Engine
1 Jace, Architect of Thought
1 Tasigur, the Golden Fang
2 Blood Moon
2 Dispel
1 Counterflux
1 Spellskite
2 Anger of the Gods
1 Izzet Staticaster
1 Rending Volley
1 Kolaghan's Command
This build is set up to combo quickly while still having the ability to grind with Tasigur, Snapcaster Mage, Cryptic Command and Kolaghan's Command. Post-board there are many game plans you can set your deck up to execute. Whether you're trying to combo, lock your opponent out with Blood Moon, answer small creatures, or grind your opponent out with powerful cards like Wurmcoil Engine and Keranos, this deck can pull it off.