Modern is the format where anything goes, and that's been borne out by the wealthy of decktypes in the Day 2 field. Still, there's good information to be had, here. Let's tuck in. First, the Big Four Decks, those expected to be most popular this weekend. Together they number 139, good for half the field.
Birthing Pod - 32
If Modern has a boogeyman, Birthing Pod is it. When it fires on all cylinders it looks like some bizarre hybrid of a one-card combo deck and a control deck that plays the perfect card every turn. When it doesn't, it looks like someone shuffled up a pile of rares from ancient drafts and called it a day. The Melira-Pod version is most popular, but Kiki-Pod is here too, and everyone seems to have tailored their maindeck to feature their pet fun-of.
The Deck Formerly Known as Affinity - 26
This is the format's signature explosive aggro deck. Litter the board with cheap creatures, and then supercharge them with Steel Overseer, Master of Etherium or Cranial Plating. Subvert lifegain strategies with the Arcbound Ravager / Inkmoth Nexus kill. Get lots of time between rounds to read your favorite penny dreadful.
Splinter Twin Decks
Basic Blue-Red - 21
Tarmo-Twin - 10
Splashing White - 4
Perhaps a consequence of the format's diverse nature, players are favoring the dedicated Blue-Red version, which allows for a faster, more consistent kill. Another deck that feels profoundly unfair when it's working. Though, as we see below, it has competition as far as being the combo deck to beat.
Whiterock - 20
Classic Jund - 16
Straight Black-Green - 10
These decks all key off a combination of black's powerful hand disruption suite, the cumulative advantage offered by Dark Confidant and Liliana of the Veil, as well as the ubiquitous Tarmogoyf. The most popular version now touches white for the power of Lingering Souls, and occasionally Sorin, Lord of Innistrad, but the tried and true Jund still has many backers. Man-lands like Stirring Wildwood, Raging Ravine and Treetop Village help finish off games once both players are out of resources.
Next we have the surprise successes, a trio of decks that put up big numbers in Day 2.
It's hard to argue with success, and this deck got a big boost when Shahar Shenhar piloted it to victory at the World Championships. The Geist versions play more like aggro-control decks, playing powerful threats and stopping the opponent's plan. Those without play the pure control role. However, beyond a core of expected cards, there is a lot of variety to be found across builds. Keranos, God of Storms seems to be something of a breakout hit.
Scapeshift - 22
The format's other big combo deck, Scapeshift is divided between versions with Prismatic Omen and without. These decks play a number of acceleration spells, defend themselves with countermagic, then try to resolve a lethal Scapeshift into Valakut and mountains. Winning without Scapeshift is very difficult, however, and Blood Moon is an absolute nightmare.
Burn - 20
Now here's a group of people singing in near-perfect harmony. Where other archetypes are variations on a central theme, the Burn deck allows little room for artistry. Goblin Guide and Eidolon of the Great Revel provide consistent damage while also not being completely blank against removal, and then you have a compact package of the best in controlled pyromancy. Sometimes called "The Seven-Card Combo Deck" because if it draws seven spells, you're dead.
Next up are the decks that put small but notable numbers of players into Day 2.
Tron - 12
These are almost all the well-known Green-Red Tron decks that use Sylvan Scrying to assemble Urza's Power Plant, Urza's Mine and Urza's Tower and dominate the game with haymakers. Samuele Estratti bucks that trend by playing Mono-Blue.
RUG - 6
Mostly these are the Red-Blue-Green Delver decks of yesteryear, but one or two are RUG in colors only.
Delver/Young Pyromancer - 6
Merfolk - 5
Bogles - 5
The Hexproof Creature + Enchantments deck that almost made Reid Duke a World Champion.
Living End - 4
On paper it's sometimes hard to see how this deck could be good, but Living End really is that powerful a spell.
Infect - 4
No blocks? Okay, you're dead.
The Rogues' Gallery - 33
You want more archetypes? Well we've got more: Esper Control, White-Black Weenies, Blue Moon, Soul Sisters, Cruel Control, Storm, Amulet of Vigor, 8 Racks, Ad Nauseum, Krark-Clan Ironworks, Zoo, Counter-Cat, Through the Breach, Loam, pure White Weenie, pure Blue-White Control, pure Delver, Hate Bears, and a deck based around "Haakon, Stromgald Surge" (Emperor Haakon?). We're not kidding when we say you can play whatever you want and win, provided you're willing to put in the hours learning your matchups and polishing your sideboard.