Playing a control deck means playing the opposite game of an aggro deck. Where an aggro deck plays one mana-efficient threat after another for the fastest victory, a control deck is looking to answer an opponent's threats and make the game go long. In that long game, the control deck uses card-drawing spells to out-resource an opponent, clearing the way to play a large, game-ending threat that the opponent can't deal with.
The problem that control decks often face is having relevant and mana-efficient answers to the threats opponents will play. Control decks must tune their answers in the shifting tournament meta-game to have the right threats to cover not only aggro decks, but combo, midrange, and other control decks! It's a lot to cover, so playing a control deck often means being highly attuned to what decks you are likely to face and using the correct cards in your main deck and sideboard to counter them.
Aether Revolt provides comfort to the control player. Not only does the set bring some truly great finishing cards, it comes with a host of efficient answer cards that work against a variety of strategies.
These are some of the top control cards in competitive Standard. Understanding these cards and why they are good will help you tune your control deck.
Herald of Anguish
Herald of Anguish is worth playing on the late game even without a reduction in its base cost. It's a 5/5 flying creature that removes cards from your opponent's hand and can remove creatures on its own, making it a threat with its own built-in answers! With improvise, Herald can be cast even earlier. Better yet, you can cast the Herald of Anguish when you normally would, but then have mana to protect it with countermagic!
Even without triggering revolt, Fatal Push is an efficient removal spell in the early game. Instant-speed, one-mana removal is about as good as it gets and makes it hard for aggressive decks to outpace you. That you can hit bigger creatures with the revolt trigger is just a sweet bonus—though note that having artifacts and Herald of Anguish lets you do this easily!
The power of countermagic is that it provides a universal answer to your opponent's threats; you can answer almost any spell as it is being cast. The problem is that countermagic usually can't do anything about permanents already on the board. Disallow circumvents this dynamic by allowing you to counter activated abilities and triggers. You can stop an Aetherworks Marvel from throwing Ulamog on the board or shutdown a Westvale Abbey. You can even blank a planeswalker for a turn. All this in addition to stopping a spell from even being cast.
Baral, Chief of Compliance
Baral serves multiple purposes in a control deck. He blocks creatures in the early game, he reduces the cost of your instants and sorceries, and he allows you to filter your hand with his loot effect. It's rare when we get cards that reward control players for playing countermagic, so Baral deserves attention from control mages everywhere. Playing Baral on turn two opens many plays that control players don't normally get. Baral can supplement almost any control shell, but seems likely to work very well with a counter-heavy mono-blue control strategy.
People have compared this to Mana Leak, but I think of it a little more like Circular Logic, in that it requires you to invest in other cards before getting a more efficient cast. Like the best of the improvise cards, Metallic Rebuke works fine as-is (we've been using Spell Shrivel pretty happily in Standard), but gains more and more value with artifacts to decrease the cost. When you are able to make an opponent pay three extra by spending only one mana, that's a great place to be.
Cards to Try
These cards don't dominate the Standard scene . . . yet. Each has unique potential and is worth trying if you like to go off the beaten path.
Not much white has been mentioned so far, but it's worth noting a card that exiles all artifacts in an environment that will reward the casting of many artifacts! Consulate Crackdown will be particularly rewarding against decks that generate lots of token artifacts in the form of Servos, Thopters, and Clues. Your opponent's investment in generating these tokens will be lost forever, even if they get rid of Consulate Crackdown. While the metagame will have to be slanted heavily toward artifact decks to make this a main deck card, it almost certainly deserves a spot in a control mage's sideboard if she plays white.
Trail of Evidence
Improvise reduces costs based on the artifacts you play. What if you had an enchantment that allowed you to make Clue artifact tokens as part of casting instants and sorceries? Trail of Evidence requires you to "take a turn off" to cast it, similar to Metallurgic Summonings. In return for the investment, you can generate Clues very easily, using them to maintain momentum through card draw or powering improvise spells like Whir of Invention or Herald of Anguish.
Exquisite Archangel is the ultimate comeback effect. Reversing a loss and going back to your starting life total is likely all a control deck needs to win many close games. Control players have used Linvala, the Preserver as a comeback card, and this effect is even more powerful in some ways. The downside of the card is that it is expensive at 5WW and subject to removal, but a control mage who finds ways to mitigate the expense through cost reduction (Inspiring Sanctuary) or through reanimation (Rise from the Grave or Ever After) might find big rewards.
Dimir Improvised Control
There are many ways to build control decks with blue and black, but one of the most powerful builds uses cheap early artifacts with improvise spells to get threats and answers at cheaper rates. This allows a control deck to do more per turn than it normally can. Being able to cast Reverse Engineer for UU or Herald of Anguish for 2BB strengthens a control deck's middle and late game, making it harder for other decks to keep up.
Inspiring Sanctuary is a card that lets us turn all our non-artifact spells into improvise spells as well, getting even greater efficiency! This is powerful enough that we want Trophy Mage to help us cast it consistently.
Eventually we want to cast Herald of Anguish to squeeze our opponent's hand and creatures, but we also wouldn't mind a cheap 4/4 hexproof creature like Bastion Inventor to assist or simply run interference for us.
Blue doesn't have the hard removal of the other colors, but it has cards that bounce and delay along with countermagic to disrupt an opponent's tempo long enough to win games. Blue can block with cards like Shielded Aether Thief and Aether Theorist, gaining energy and card advantage along the way. The energy can be used to control the board with Confiscation Coup and Dynavolt Tower. Crush of Tentacles, Baral's Expertise, and Engulf the Shores can deal with flooded boards long enough to start taking extra turns with Gonti's Aether Heart and Part the Waterveil. You finish games out with awakened lands, stolen creatures, or Aethertide Whale.