Affinity – One of the most aggressive decks in Modern, Affinity plays a number of ridiculously cheap (sometimes free) artifact creatures, enhances them with Master of Etherium and Cranial Plating, and dishes out lethal damage in ridiculously short order.
Amulet – There are two varieties of this potent combo deck, both of which take advantage of Amulet of Vigor and a plethora of methods of putting multiple lands into play to generate a very large amount of mana. One version of the deck uses this to cast Hive Mind followed by a Summoner's Pact which the opponent won't be able to pay for, losing them the game. The other takes advantage of Primeval Titan, Slayer's Stronghold, and Sunhome, Fortress of the Legion, to deal a single lethal attack, which it is surprisingly capable of dishing out as early as turn two!
Storm – The basic U/R version of this deck abuses Pyromancer Ascension and a deck full of cheap or free card-drawing and mana generation spells to rifle through the deck, generating a giant spell count that culminates in a lethal number of Grapeshots thanks to the storm mechanic. The other version generates the storm count by playing Angel's Grace before drawing every card in the library, which sets up the deck to use many of the same mana generation tricks.
Blue Moon – An innovative new Modern deck bursting onto the scene here at Pro Tour Born of the Gods, Blue Moon is a U/R control deck featuring Blood Moon and Spreading Seas for resource control, Threads of Disloyalty and Lightning Bolt for creature control, and Master of Waves and Batterskull for the kill. Attacking Modern's mana bases has proven to be a potent strategy in the past, and Blue Moon seems like the newest incarnation of this type of deck.
Burn – Wait, Lightning Bolt can hit creatures? No one told that to the players running Burn in Modern. If it is red and can go to the face, you can bet it will. Most of these decks are also adding black for Bump in the Night. Because doing it with just red spells would be too easy.
Faeries – This event marks a homecoming for two members of Magic's royal family. The first of these is Faeries, a U/B control deck centered around the tribal Faeries cards from Lorwyn. Thanks to the prevalence of flash, most Faeries players tend to play more on their opponents' turns than their own. The notable exception to this rule is the reason for Faeries's resurgence: the recently unbanned Bitterblossom.
Hexproof Auras – Some decks just don't want to play nice, and Hexproof Auras is one of them. One part a creature with hexproof (like Slippery Bogle), four parts power-enhancing auras (think Daybreak Coronet), one dead opponent. The deck has a high amount of variance, but the hexproof makes it one of the hardest decks to stop once it gets going. Go big or go home. That is Hexproof Auras's motto.
Infect – Another of the creature-based combo decks in the vein of Hexproof Auras, Infect wants to play one of the one-drop or two-drop infect creatures, attack with it, and pump it to deliver a lethal dose of poison in one attack. It's a little more fragile than Auras, but it has the potential to end the game even faster.
Jund – One of the old-school kings of, well, every format, Jund was rumored to be dead with the banning of Deathrite Shaman, but there are a still a large number of players touting its viability. Jund is basically all of the best green, red, and black cards Modern has to offer, all smashed into one midrange-y control-ish deck. Jund is the epitome of an attrition/disruption deck, built to mess up an opponent's plan, regardless of what it may be. Between Thoughtseize, Liliana of the Veil, Maelstrom Pulse, and Scavenging Ooze, no avenue of attack is safe from Jund's disruption. The price of this power is one of the most vulnerable mana bases in the format.
Kiki Pod – One of the two versions of Birthing Pod combo decks, Kiki Pod uses the Pod to fetch up a combo consisting of Kiki-Jiki, Mirror Breaker, and either Pestermite, Restoration Angel, or Deceiver Exarch, making a very large number of tokens. I'm sure you can figure out what to do once you've got them.
Melira Pod – The other of the Pod decks in Modern, Melira Pod takes advantage of the interaction between Melira, Sylvok Outcast, and persist. Thanks to Melira, creatures with persist never get their -1/-1 counters when they return to play, allowing them to be cycled as many times as you'd like with the appropriate sacrificial outlet. Viscera Seer provides this, allowing Kitchen Finks to become a lot of life or Murderous Redcap to become a lot of damage.
Living End – One of the few graveyard-based decks in Modern, Living End abuses the cascade mechanic, which allows the Living End player to cast a card like Ardent Plea or Violent Outburst (which can be cast at the end of an opponent's turn) to cascade into Living End, the only card in the deck cheaper than three mana. This is preceded with a series of cycled creatures, cards like Street Wraith and Monstrous Carabid, which then make their way into play. The deck isn't often lethal on the first attack, but the second usually gets the job done. The scary part? The deck can pull this off on the second turn with the right draw...
Merfolk – Now that Master of Waves and Thassa, God of the Sea, have been printed, Merfolk has been given a real boost. Merfolk is a blue-based aggressive deck that has historically been favored for its ability to offer both aggression and disruption. This makes it incredibly powerful in a format as combo-centric as Modern can be. Between Cursecatcher and cheap countermagic, Merfolk decks are usually able to keep opponents off-balance just long enough for a sea of Merfolk to overwhelm their defenses.
Scapeshift – Another of the big combo decks in Modern, the most commonly-seen version of Scapeshift uses Prismatic Omen to turn all of its lands into Mountains, casts mana acceleration to get lands into play, then casts Scapeshift. This Scapeshift searches up the same number of lands that are sacrificed to it, turning them into copies of Valakut, the Molten Pinnacle, and the proper number of other lands. Thanks to the Omen, this is almost invariably lethal. Considering the deck often runs Izzet Charm and Cryptic Command as well, it is equipped to protect itself against almost anything.
Tron – Built around the holy trinity of Urza's Mine, Urza's Power Plant, and Urza's Tower (colloquially referred to as the Urzatron), this is a big mana deck. Many of the cards in this deck are dedicated to assembling the pieces, while the rest are big-mana colorless spells, like Karn Liberated and various members of the Eldrazi.
Twin – Twin decks run a very similar engine to Kiki Pod, looking to assemble some combination of Kiki-Jiki/Splinter Twin and either Pestermite or Deceiver Exarch to generate an infinite number of creatures. There are versions of this deck that touch white for Restoration Angel and Village Bell-Ringer, adding a touch more versatility to the deck.
W/U Control – One of the old standards of Magic, WU Control is exactly what it sounds like: a slow, grinding affair. Much like the W/U/R Flash decks, the deck runs some combination of Snapcaster Mage, Restoration Angel, and Geist of Saint Traft to kill opponents and keep the game under control. This core is supported with a traditional complement of Sphinx's Revelations, countermagic, and Supreme Verdicts.
W/U/R Flash – This deck is a bit more aggressive than the W/U Control deck, tending to play even more creatures and less of the late game cards like Sphinx's Revelation. The addition of red allows for cards like Lightning Bolt and Thundermaw Hellkite to make an appearance, both of which are incredibly powerful ways to just end the game. The name flash derives from the keyword ability found on the core of Restoration Angel, Vendilion Clique, and Snapcaster Mage.
Zoo – Zoo is the other member of Magic royalty to make a resurgence here at the Pro Tour, again due to a fortunate unbanning. Wild Nacatl, once banned to promote diversity among the aggressive decks of Modern, is once again free to roam the open Plains (and Mountains and Forests) of the Pro Tour. Zoo decks were certainly played during the Nacatl's hiatus, but the one-mana 3/3 creature really was the glue that held the deck stuck firmly in the top tier. There are three versions of the deck, each a slight variant. Traditional Naya Zoo pairs the Nacatl with other cheap and aggressive creatures in green, white, and red. It can run from the ridiculously aggressive decks with Loam Lion a number of one drops to Big Naya, which reaches all the way up to Thundermaw Hellkite. The Domain Zoo decks dip into some combination of blue for Snapcaster Mage and Geist of Saint Traft or black for Dark Confidant. The final version of the deck, CounterCat, is similar to a green-based version of Merfolk, trying to play a few aggressive creatures before disrupting just enough to get the job done.