About a week ago Wizards of the Coast announced that they were truncating the extended format. Rather than being decks from the past seven years of cards, new extended only covers the last four years. There are two major effects to this change; first, the price of a number of old extended staples (Ravnica Block Dual lands, Dark Depths, etc), dropped like the economy. I'm generally fine with that, as I had very few of those staples, and quite a few more for new extended. Secondly, a whole new format for deckbuilding has opened up.
A whole new format you say? With very few known constraints? Excellent. Even if I don't have the cards to actually build most of these decks it's still a whole barrel full of fun to speculate about the format. So let's get to speculatin'!
First off: Faeries.
Faeries was the deck that dominated standard for the two years it was legal. While there were certainly other contenders, Faeries was the standard barrier to entry. If your deck didn't have a decent chance against the fey, then back to the casual room with you! The deck leveraged a punishing suite of synergies to work as either a fish deck when fighting control decks or a control deck when fighting aggro decks. At it's heart, Faeries is dependent on the interaction between Spellstutter Sprite, Bitterblossom and Mistbind Clique. All three provide bodies on the ground while disrupting the opponent. In addition, Faeries needs all four Cryptic Commands as a universal answer, and some number of Mana Leaks. From there you've got a couple more options in what you're using as a draw engine; Jace Berelen, Esper Charm and Ancestral Vision were all popular before. Jace the Mind Sculptor and Jace's Ingenuity are pretty obviously also contenders.
Faeries is the obvious contender, I don't want to go too much further into it. Suffice to say that whatever the metagame shakes out to be it'll have some percentage, and thus I'll be looking to include things like Great Stable Stag or Volcanic Fallout in any decks I'm designing to give them a better matchup.
Moving along, our next contender is the burn deck. This showed up in the last extended as a collection of the most efficient burn spells to give you a decent clock. Never really that good of a deck, it didn't lose much in rotation, so it's worth looking into.
4 Lightning Bolt
4 Shard Volley
4 Goblin Guide
4 Rift Bolt
4 Keldon Marauders
4 Lash Out
4 Searing Blaze
4 Flame Javelin
Two creatures, a 2/2 haste guy for R and a 2 mana burn them for five that can have three of it's damage blocked. 3 3 damage for 1 mana spells. 2 4 damage for 3 mana spells. The only thing that even looks like an innovation here is Lash Out and Searing Blaze; as they will sometimes kill a creature AND hit the opponent they simultaneously buy you some more time to enact your game plan and make sure you don't need to use that time. There might be some nonbasics worth running too (Ghitu Encampment and Mutavault for manlands, Valakut or Keldon Megaliths for more burn, for example.)
Moving Along, what about Zoo?
Zoo loses a lot in that Wild Nacatl and Loam Lion will have a much harder time finding their appropriate lands since the Ravnica Duals rotated. But as long as there are worryingly efficient creatures they still have options. A couple possible shells:
1) Boros Deck Wins. Hasn't been doing that well in standard lately, but it's possible. Steppe Lynx and Plated Geopede powered by Zendikar Fetches and backed up by Figure of Destiny and a burn shell like the one I listed above.
2) Screw it, going Domain Zoo regardless. The burn of Tribal Flames and Exploding Borders being backed up by Prismatic Omen. Allows you to play Wild Nacatl, Loam Lion and Might of Alara. Seems janky.
3) Go Naya.
4 Tarmogoyf (how long did you think I could go without mentioning him?)
4 Quirion Dryad
4 Knight of the Reliquary
4 Boggart Ram-gang
4 Bloodbraid Elf
4 Lightning Bolt
4 Punishing Fire
4 Colossal Might
Lands (Including Grove of the Burnwillows)
Ok, that's obviously a pretty rough list. In particular the Quirion Dryad package might be too clever for it's own good. But each of those creatures packs a wallop, and everything else in the deck pumps Dryad, including repeated Punishing Fire. Knight of the Reliquary searches up redundant groves, and you can fit some pretty decent manlands in the mix. (Treetop village, Stirring Wildwoods are on color.)
Also on the contender list for aggro, we might see a resurgence of Kithkin. The little white men held their own in their standard format, splashing into black, red or green as the metagame called for it. The main engine of Windbrisk Heights and Spectral Procession is still very good, and there is plenty you can do with that shell. My guess is that the deck will be better as a black/white tokens iteration, if only because Urborg, Tomb of Yawgmoth makes splashing so easy. Turn three spectral procession, turn four drop Urborg and activate Mind Sludge from under your windbrisk heights, stripping their hand.
Moving into the realm of midrange, Jund will still probably be a contender. It always struggled against faeries, but a wider card pool will benefit it more. The Punishing Fire combo and yes, Tarmogoyf ought to boost it's power level.
Also, it might be possible to build a competitive version of Doran Rock. Doran, the Siege Tower benefits from having a relatively easy mana base (Murmuring Bosk is fetchable by Verdant Catacombs), and the non-linear nature of the deck benefits from recent printings more than, say, faeries. Wall of Omens in particular looks neat next to Mr. The Siege Tower. The deck has card drawing (Harmonize, Sign in Blood), efficient beaters (Putrid Leech, Doran, Tarmogoyf, Chameleon Colossus), excellent removal options (Path to Exile, Maelstrom Pulse, Doom Blade), disruption options (Duress, Thoughtseize, Fulminator Mage, Gaddoc Teeg), and generally anything else you want, 'cept counterspells. Unless you want to run Dash Hopes. Hmm...
The same shell as above, only substituting out Keldon Marauders and Shard Volley for Dash Hopes and Browbeat. Dash hopes will hopefully let you counter their spell, because they don't want to lose five life against a burn deck. Similarly with Browbeat, either three cards or five burn for three mana is a deal. Yeah, probably not the direction you want to be taking this deck.
Back on the midrange, you know what deck really gains from the new format? My Reveillark deck. (And part II). The final list almost entirely within new extended; swap out Eternal Witness and Ninja of the Deep Hours for ponders, maybe Venser as well, swap out a couple Ravnica Duals for 10th edition painlands (or redo the manabase with less Ancient Ziggurat and more filterlands) and we've got a fully functioning extended deck. Awesome
You could also make a traditional 5 color control deck, much like the ones that also faced off against faeries. As usual, the heart of the deck is the Vivids/Reflecting Pool package that lets your mana get crazy fixed. Previous versions included Cruel Ultimatum as it's haymaker, cryptic commands and cloudthreshers. Wrath of God for removal and Esper Charm or Jace Berelen for card drawing. As the deck can quite literally stretch for any card in the format, it gains a whole lot of new options with the addition of two more years of sets. Esper charm in particular has an unfriendly casting cost, and isn't the best card drawing. Ancestral Visions, for example, is a much more appealing option. All that as it may be, this deck is probably superior designed as a response to the metagame. As it potentially has the tools to overcome any sort of decks in the metagame, it's best designed in response to a known metagame.
Want one better? Future Sight saw the printing of Glittering Wish. While all the wishes got worse with the M10 rules changes (still annoyed about that particular change, by the way), Glittering Wish does allow us to construct a wishboard for a 5 color deck. Some notable cards:
Nichol Bolas, Planeswalker
Oona, Queen of the Fae
Figure of Destiny
Knight of the Reliquary
Doran, the siege Tower
Or you know what? Take a gander through gatherer yourself; there were five sets with a strong multicolor theme in the past four years (Shadowmoor, Eventide, Shards of Alara, Conflux, Alara Reborn), and they offer some powerful and interesting multicolor cards.
The question remains, what's the best way to build this particular deck? Well, it's gotta have your traditional five vivids/pool manabase. Additionally, since you're expecting to cast multicolored cards rather than heavily single colored cards, the filter lands get slightly worse. Cloudthresher for 2GGGG and Cryptic Command for 1UUU heavily incentivizes you to play Flooded Groves since it can provide UU on one turn and GG on the next. Playing a deck with Gaddoc Teeg and Meddling Mage doesn't nearly as much, since you need the lands to make two of three colors, and therefore you need the right land if you're doing it off of the filter and not another source. I might have to go into that in more detail later.
As far as the rest of the main deck goes, it's gotta support 4 Glittering Wish at GW. The deck lends itself otherwise to a control deck, so you probably want four wall of omens and four kitchen finks in the main too. At this point I'm thinking it might be worthwhile to staple a wishboard onto a Doran Rock Shell, which would be awesome. But again, you can vary this strategy to whatever the metagame has. Also note that it gives you the option of leaving your clunky finisher cards in your sideboard, where they won't clutter up your opening hand.
Moving along, another Reveillark deck to note is Blue White 'lark, or UWr 'lark. Imagine this set of plays:
Turn one suspend Gargadon
Turn two suspend Riftwing Cloudscate
Turn three play Aether Adept, bounce a land
Turn four play Venser, Shaper Savant, bounce a land
Turn five Riftwing cloudscate comes into play, bounces something. Play Reveillark, sac Venser and Adept to the gargadon and bounce whatever permanents they have left.
Ok, Magic Christmas land, yeah, I know. Still, you can manage an astonishingly powerful series of plays with those cards, noting that there are others that slot in well in the mad bounce plan, or otherwise interact powerfully. Cryptic Command, Nevermaker, Body Double (the old infinite combo) or even wall of omens.
While I'm talking Combo, let's take a look at the combo decks available in the format.
First off: Seismic Swans. Use cascade cards to cascade into Seismic assault and Swans of Byrn Argoll. Direct land to deal two to swans, drawing you two cards and hopefully enough land to keep tossing it at the swans for more cards and eventually ten land to just burn out your opponent. Has game if it doesn't assemble it's combo; being able to use seismic assault to control the board and able to run numerous manlands. Gets better with Worldwake manlands.
As most combo decks, or at least combo decks that are allowed to survive bannings, Seismic Swans tends to be a trick deck to pull out when the metagame has forgotten about it. If people are starting their sideboards with four pithing needles, you probably want to move on to another combo.
Next up, scapeshift. This deck lost a lot of resiliency with the ravnica duals. Now to be sure to kill someone with scapeshift you have to run enough mountains in your main deck, while still being able to pay GG. One option that a slower extended might allow is using Prismatic Omen as a combo piece. Drop Omen on turn six, and immediately follow it up with a scapeshift. Search out six lands, two of which are Valakut. Since they're all mountains, each Valakut will trigger six times, burning your opponent out. The deck's still pretty weak to counterspells though.
Another contender is, well, anything that gets you Emrakul, the Aeons Torn into play sooner than turn 15. Jhoira of the Ghitu, in Time Spiral block, allows you to suspend him for four, and it still counts as casting him. Or drop him under a hideaway land and fulfill the condition. (Hmm... spectral eldrazi? a mono white combo deck? Madness.)
Yet another option hinges on exploiting Oren Rief, the Vastwood and it's interaction with persist. Take a look at this:
4 Kitchen Finks
4 Woodfall Primus
4 Greater Gargadon
4 Dramatic Enterance
4 Summoning Trap
12 Ramp Cards
4 Oran Rief, the Vastwood
20 other lands, as necessary.
Or some such. Get finks into play, gain two life. Block with it, persist it, gain two life, and then put a counter on with the Vastwood. +1/+1 and -1/-1 counters cancel each other out, finks has another lease on life as a blocker, and another persist for even more life. You can reset multiple at once with a single vastwood too. This goes double for Woodfall Primus, which destroys a noncreature permanent each time it persists. At that point you'll have a harder time trading it away in combat, so you want a Gargadon suspended to sack and blow something up as desired. OR whenever someone tries to Path to Exile it.
Dramatic Enterance lets you cheat on the mana costs. Summoning Trap will very seldom whiff with twelve legitimate game ending threats. And if faeries are as played as people expect you might get to cast it for it's trap cost.
I'm going to end with an archetype near and dear to my heart: Goblins.
Lorwyn block being tribal provided quite a number of interesting goblin cards. In addition, there are powerful cards that have been printed in other sets surrounding. Let's take a quick rundown of options:
Stingscourger (yes, one of my favorite cards, as I've mentioned.)
Mogg War Marshal
Wort, Boggart Auntie
and all sorts of lesser goblins with more specific abilites. Additionally there's all that excellent red burn I listed above. Still not enough? Auntie's Hovel makes splashing for Black relatively painless, which gives disruption options: Thoughtseize, Duress, Inquisition of Kozilek, Thought Hemorrhage, etc. I've actually got a legacy goblins list (rogue build) that's fairly similar to what's available. Lemme list it quick.
4 Goblin Guide
3 Tattermunge Maniac
3 Goblin Bushwhacker
4 Mogg War Marshal
3 Goblin Chieftan
1 Mad Auntie
2 Greater Gargadon
4 Lightning Bolt
4 Flame Javelin
24 assorted lands
The sideboard is metagamed differently, but most of the components can be found in new extended.
Those are all the decks I'm going to cover currently. There are doubtless more options out there, and more card interactions than I've heretofore thought of. Have fun brewing!