What are the Decks to Beat?
The Decks to Beat are the top decks in the format. These are the ones that you should expect to play against in tournaments and what you should test against. The Decks to Beat are based on popularity, so it will usually be the most powerful decks, but not always.
Thread links and short descriptions:
Affinity uses cheap, efficient creatures with Mirrodin block's Affinity ability to quickly power out beats and keep the pressure on. It uses Arcbound Ravager, Frogmite, and the like for quick beatdown, in addition to using Thoughtcast to gain card advantage. Some versions also use Red for Atog and Fatal Frenzy to end the game in a flash.
Affinity Primer by blackcat77
Mono red burn is an aggro deck that tries to bring down its opponent's life total to 0 as fast as possible. To achieve this, efficient burn spells make up most of the maindeck. It is slightly slower than other aggro decks, but it makes up for this with a painless mana base and making its opponent's removal dead, or, at the very least, have the few creatures that it runs do damage when they die.
Burn Primer by iamajellydonut
Deathcloud is a deck similar to The Rock, in that it combines disruption, mana acceleration, and big threats to create a powerful deck. The printing of Lorwyn’s Planeswalkers, particularly Garruk Wildspeaker, allowed Rock decks with Death Cloud to become very popular and powerful decks. Death Cloud has no effect on the Planeswalkers, so you have a very powerful card on your side of the board while your opponent has nothing. After that, winning is rather easy. Tarmogoyf and Ravenous Baloth also give the deck powerful anti-aggro tools and an alternate win-condition.
Deathcloud Primer by blackcat77
Elves! is a combo deck that uses Glimpse of Nature to draw through its deck while producing large amounts of mana through Heritage Druid or Birchlore Rangers. Nettle Sentinel is particularly powerful with Heritage Druid and Birchlore Rangers, due to its untapping ability. Summoner’s Pact and Chord of Calling get the pieces you need to start the combo and let you continue it if you draw them while going off. Once you have built up an army of elves, you can win with a variety of cards, the most popular being Predator Dragon.
Elves! Primer by Lynx_The_one
Faeries began as a humble tribal deck in post-Lorwyn Standard before becoming a dominant force in Block and Standard with the inclusion of Bitterblossom from Morningtide. The Extended version of the deck is a very different animal, but the deck still relies on a number of powerful Faerie synergies, while playing a popular suite of the most powerful blue spells in the format. Spell Snare, Mana Leak, Spellstutter Sprite, and others control your opponent while you drop threats like Vendillion Clique and possibly Bitterblossom and Mistbind Clique.
Faeries Primer by Narcissist
Next Level Blue
Next Level Blue is a Blue control deck that splashes Green for Tarmogoyf. It uses cards like Spell Snare, Stifle, and Remand to gain lots of tempo early, then drops a Goyf and beats for the win. Vedalken Shackles and sometimes Threads of Disloyalty are used to steal the opponents’ best creatures. Ancestral Visions provides excellent card advantage.
Next Level Blue Primer by thehouse
Reliquary Loam is a variant of The Rock that uses Life From the Loam along with Raven's Crime and cycling lands to create a powerful card drawing engine. It also uses powerful disruption like Path to Exile and Thoughtseize. Tarmogoyf, Knight of the Reliquary, and Kitchen Finks provide the beatdown.
Reliquary Loam Primer by RathiAssassin
RGW Zoo, as the name implies, is an aggro deck using Red, Green, and White. It uses efficient creatures and burn to win the game very quickly. This speed makes it arguably the best aggro deck in Extended and gives it a great matchup against control and other aggro decks. Recently, it has become more popular than Domain Zoo due to its improved matchups against Faeries, Burn, and Deathcloud.
RGW Zoo Primer by mntwinsfan
TEPS, or The Extended Perfect Storm, refers to a small group of decks that seek to win the game through a big Mind’s Desire. It uses card drawing and mana acceleration to fuel Desire. Casting a Mind’s Desire with a storm count of 5 or more is almost always enough to win the game. Win conditions vary, but Tendrils of Agony and Grapeshot] + [c]Pyromancer’s Swath are the most common.
TEPS Primer by mishima_kazuya