About the Deck
Keeping board control means that as long as your opponent doesn't have charge, you get to control which creatures fight with which creatures. That's a big advantage. You want your 1/2 to fight his 1/1, your 2/1 to fight his 3/2, and your 5/2 or 5/3 to fight is 4/5 or 6/5. If your creatures are out first, you get to match up the fighting in your favor.
If you keep killing your opponent's creatures, you can get an advantage by "trading up." That means you trade a smaller or cheaper creature for his new creature. Frequently you can trade an old creature that already attacked several times for a new creature that your opponent just spent all his mana on. How? The best options are Shattered Sun Cleric, Dark Iron Dwarf, and Defender of Argus, which enable your older creature to deal more damage. You can also get extra damage from Demonfire, Knife Juggler, Soulfire, Power Overwhelming, or Mortal Coil. Also, if you have multiple weak creatures, you can trade them into a new creature and still get a good deal thanks to your card drawing effects like Novice Engineer and Life Tap.
Shattered Sun Cleric and Dark Iron Dwarf (which we'll call the buff creatures) are very powerful cards and this deck aims to take full advantage of them. In general, if both decks play a bunch of creatures, but I have buff creatures and my opponent doesn't, I will win because the buff creatures let me make really favorable trades in creature combat. If we both have buff creatures, then whoever gets board control has a big advantage because he will have creatures to buff while his opponent won't have anything to use his buffs on. The result is that most good creature decks use buff creatures, because they are so strong, and if everyone uses them then whoever gets board control has a big advantage.
So if both sides want board control so their buffers are more effective, and so they can control combat, what do you do to get it? You start playing creatures first! You need cheap creatures and cheap kill spells. And that's where the Warlock hero comes in. Warlock has six good 1 mana creatures (Blood Imp, Flame imp, Voidwalker). By using the Warlock 1 mana creatures in addition to the netural Argent Squire, we can achieve a deck with eight 1 mana creatures. That is more than any other standard deck is currently able to use effectively because Warlock has the best class-specific set of 1 mana creatures. We also get Soulfire, Mortal Coil, and Demonfire for cheap early removal.
There is a second reason for playing Warlock and it's Life Tap. If you play a lot of 1 mana creatures, what do you do later in the game? Other heroes risk running out of steam later in the game if they have too many early game cards. But with Warlock, playing lower mana cards means you have more mana left to draw cards with Life Tap, so it's much harder to run out of momentum.
It's rare to get bad hands with this deck. Nineteen cards from 0-2 mana mean you are virtually always going to draw good early game cards right from the start.
For the higher mana cards, they are eleven of the highest quality cards for 3+ mana. There’s no fear of losing steam in longer games because you can draw cards with Life Tap and the presence of Jaraxxus. You start off strong but you can win later too. This deck is strong all around!
This is not an all-in suicide rush deck. Be careful about area of effect spells and use Life Tap instead of overextending. Know what board clear spells your opponent may play on which turn and buff some of your creatures' health to live through them. As a bonus, Argent Squire can live with her Divine Shield. Also, don't be shy about trading your creatures for enemy creatures to lower the effect of board clear spells. Remember! Don't put out more creatures than necessary.
One of the goals of the deck, if you don't win early, is to keep the initiative until turn 9. If you still have the initiative at turn 9 and play Jaraxxus, you should win. Jarraxus is extremely good if you end the turn you play still him at 15 hp with some creatures out, and your opponent has no creatures out. If you do not have the initiative, then you will usually die even when trying to play Jaraxxus. But fortunately this deck is great at getting the initiative early and then keeping it.
Quick Tip: Don't be too scared to attack with Blood Imps. Don't just get it killed to the Mage hero power for no reason. If you can buff it and it will cost them a removal spell or creature to kill it, then go ahead and attack. Using Blood Imp aggressively reduces your vulnerability to many area of effect spells. Any time you're trading 1 mana cards for any card your opponent has, you gain the advantage. You can afford to trade off a bunch of cheap cards and draw new ones while your opponent risks running out of cards.
This deck is very good at using all its mana for the entire game. Early on, you can use all your mana because you have a lot of cheap spells. Later on, you can spend 2 mana per turn on Life Tap and then draw two cards, letting you play an average of two cards per turn. Between Life Tap and two cards per turn, you can usually spend all your mana even though the deck has a low mana curve.
Combos!
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+ It's even better if Sylvanas was already in play. Then you can use Power Overwhelming on her and attack for 9 damage (to their face, or to kill off one of their extra creatures) before she dies!
Note that if they have several creatures, you can use Soulfire to kill one so you steal the right thing, just make sure you play Sylvanas and Power Overwhelming first so they don't get discarded.
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Card Choices
The power of low cost minions!
For 2 mana creatures, Novice Engineeris selected because you get the card draw immediately and it's a good top deck when you have a lot of mana. She also has 2 health so it stands a better chance of living long enough to be buffed by Shattered Sun Cleric or Dark Iron Dwarf. Knife Juggler works well in a deck with this many low cost creatures so he gets to shoot often.
At 3-4 mana we have the buff creatures: Sun Cleric, Dark Iron Dwarf, and Defender of Argus. These are great for improving your earlier creatures to let them trade up for larger creatures or kill your opponent quicker.
For 5 mana, we have Azure Drake. Azure is a good card because you can play it and then Soulfire for 5 damage immediately. It's also a 4/4 that draws a card. The reason for only one Azure is that it takes a lot of mana to cast them and the cards they drew in the same game. After testing many games, I've come to the conclusion that 1 Azure Drake provides the best pacing for the game. We also have Sylvanas at 5 mana because she's an amazing card, especially with all the possible combos in this deck.
For 6 mana we use Argent Commander because it's such a strong card and belongs in almost every deck. The combination of Charge and Divine Shield lets you kill an opponent's creature and get a 4/3 creature of your own. It can also help finish off your opponent to end the game.
For spells, Soulfire does a great job of getting the initiative or finishing off an opponent. Mortal Coil helps control the board early or trade up while drawing a card. Demonfire helps kill your opponent's early creatures but if they don't play creatures you can still use it to buff your creatures’ health out of area of effect spell range and increase their attack for more direct damage. Power Overwhelming can help kill big creatures or help finish off your opponent and is useful in several combos. Shadowflame is a powerful card capable of killing many creatures at once. Finally,Jaraxxus gives you a huge amount of late game power once you start bringing out those Infernals.
Sideboard Options
I've considered and tested many alternative cards for this deck. Some are solid cards which I sometimes use if I know what deck I'm playing against. Others are less good and I don't recommend them. First let's consider some of the cards I would most often add to the deck against specific opponents.
Siphon Soul: This card costs a lot of mana and many opponents won't give you an ideal target. There aren’t too many ideal targets out there because any creature that is worth using a Siphon Soul removal is also a good target for Mind Control (or Sylvanas!). However, Siphon Soul is a good addition if you know you're playing against a deck with plenty of big creatures.
Acidic Swamp Ooze: There's not a lot to say here. I wouldn't use Ooze against a random deck, but I would be happy to add it if I know my opponent is using weapons. One tip is not to remove your Knife Jugglers for Ooze. Ooze is a card you will sometimes save past turn 2 to destroy a weapon, so if you remove your early creatures for ooze then you slow the deck down. More often I would consider removing Thalnos and Mortal Coil to add Oozes.
Loot Hoarder: Loot Hoarder isn't the ideal card against Mages, Rogues, Druids, and sometimes Paladins because their hero power can kill it off. It's not a disaster in that case, but it's not the best either. It works better against the other heroes so I would consider adding it in against them. Be especially careful against Priests. It's still a great card except for two major problems: Shadow Madness and Cabal Shadow Priest.
Faerie Dragon: Faerie is good against enemies who rely on kill spells, such as Mages and Priests. It's a solid alternative to Knife Juggler. The reason I normally use Juggler is because I have so many cheap creatures that I can get a lot of juggles. Also, I have plenty of other creatures that can be targeted by the opponent and their removal will still be useful even if I play Faerie Dragon.
Cards That Didn't Make the Cut
Abusive Sergeant: I like 1 mana creatures but we already have eight of them. This guy is good because he helps you trade up. But he's very weak against the Mage hero power if you don't have a Blood Imp out and he frequently dies to area of effect damage spells. I prefer Argent Squire and Voidwalker because they are more durable and Flame and Blood Imps because they are pretty amazing in general.
Harvest Golem and Scarlet Crusader: These are similar cards with 3 mana cost and have "two lives" in a sense. They are both good cards that I would consider using in other decks. However for this deck they cannot compete against Shattered Sun Cleric at 3 mana. This is a deck that has a lot of cheap creatures and focuses on taking board control so the Sun Cleric is the best 3 mana choice. The main reason I don't use Harvest and Scarlet is that I don't really want more 3+ mana cards unless they are really exceptional. Harvest and Scarlet are good, not amazing, so they won't get me to raise my mana curve, miss Life Taps, and have a less consistent first 2 turns.
King Mukla: Mukla is usually a great card on turn 3 (or 2 with coin) but the bananas are a serious problem and he's really bad when you're behind without board control. He can also be a bad card to draw later in the game so adding him to the deck would be a risky choice. Again, I currently don't feel the need to take a risk like this since the deck is so consistently strong.
Ragnaros (and Ysera): Ragnaros costs 8 mana, which is a lot. If you add him to the deck, sometimes you will draw him early on and he will sit in your hand for a while not doing anything. Sometimes he will shoot the wrong thing and then get Polymorphed. He is a powerful card for sure but I've found that having a very strong early game gives the deck the most consistent chance at winning. He's also bad against Mind Ccontrol. Ysera is similar to Ragnaros except significantly slower so don't even think about adding her.
Shadow Bolt: The problem with Shadow Bolt is that, like Mortal Coil, you don't always have a good target. To have a deck that can win consistently, it's really important to minimize the number of situational cards that will sometimes sit in your hand without doing much.
Sunfury Protector, Sen'jin Shieldmasta: These cards can be helpful against aggressive decks including Hunters with Unleash the Hounds. They are worth adding in occasionally if you know the content of your opponent's deck. But in general I don't recommend them. It's usually safer for this deck to just take the initiative and play aggressively, not try to defend with taunts.
Leeroy Jenkins, Doomguard, Succubus, Felguard, Pitlord: These are all risky cards that will sometimes win you games and sometimes be detrimental Because the deck does so well already, it's a bad idea to add inconsistent cards that mess a good thing up. Taking risks like this is currently unnecessary.
Drain Life: Drain Life is a weak card. I know some people like it, but they are mistaken. 3 mana to deal 2 damage is simply bad. Yes you get 2 life, but that isn't enough of a bonus to make up for 3 mana 2 damage being way too weak.
Matchups
Depending on the class, this deck can have from a slight less than even win rate all the way to 95% win rate. Here we'll talk about all the class matchups for this deck in order of worst matchup to best matchup. Generally, classes will do better against this deck if they have more tools available for the early game. For instance, the best matchup for the deck is against Priest while the worst is against Mage. Speaking of Mage...
Vs Mage
Be careful going below 15 life since that is close to the range of Fireball + Pyroblast ‒ being above 20 life is safer. Often you should save Jaraxxus until after they cast Pyroblast or at least Fireball on you unless you would die. Jaraxxus restores you to 15 health after a Mage burns you down, which can win you games. Watch out specifically for and play around Blizzard; if you survive early game relatively unscathed, Blizzard is one of the only ways for the Mage to get back into the game.
Vs Warlock
Some other Warlock decks use Molten and Mountain Giants plus board clears like Hellfire and Shadowflame. They also use Sunfury Protector and Defender of Argus to give their Giants Taunt. Play aggressively and kill them as fast as possible. In most matchups you have a reasonable chance in longer games but against the Giants Warlock deck you'll need to win quickly. When their first big creature comes out, you have to carefully consider whether to attack them for the quick win or kill off their creature. It will take practice to make good decisions in those situations. Keep in mind that if you leave a Giant at 8/8 and attack them, they may give it Taunt and then use Faceless Manipulator to copy it.
Also, keep in mind that the card Sacrificial Pact is the dumbest thing ever in Warlock mirror matches. Not only does it kills your opponent's demons for 0 mana while healing you for 5 health, it can even kill Jaraxxus and instantly win the game. I hope Sacrificial Pact is changed to target only friendly minions (and to heal for more like 10 health, so it's not so bad). In the mean time, Sacrificial Pact should be banned from tournaments in my opinion. When I played against other Warlocks in recent tournaments with sidedecks, we usually agree not to use it.
Vs Rogue
A Rogue who builds her deck around Sun Cleric and Dark Iron Dwarf is a tougher matchup. Their weapons are powerful but you get to draw more cards with Life Tap. Both classes are excellent in the early game, so the battle in the early game will be crucial as whoever gets momentum first will usually keep it throughout the game. As usual, focus on getting creatures out quick and killing off all their creatures. If they don't have targets for their Sun Cleric and Dwarf and you have targets for yours, then you'll probably win.
Vs Shaman
Some Shaman decks try to kill you with Bloodlust. They either use Murlocs or some other aggressive creatures. If they get lucky you will die, but it's still a good matchup. You have plenty of early game power, so just don't let them get an army built up.
Another type of Shaman uses a stealth creature, usually Stranglethorn Tiger, combined with Windury and damage boosts like Rockbiter Weapon, Flametongue Totem, and Abusive Sergeant. Like other combo decks, this deck has a weaker early game than you do. Play creatures and attack and put on a lot of pressure. If you get a slow start they might have a chance, but in a race between your aggression and them pulling off their combo, you will usually win.
Finally, there are slow control Shaman decks. You'll take the initiative easily at the start. Kill their totem every turn and never let them attack with any creatures. Your board control will make their buffs (like Flametongue Totem) useless and prevent Mana Tide Totem from providing value. When they play Earth Elemental, spend what you have to in order to kill it immediately and keep attacking. Don't worry about trading Soulfire and a creature (3 cards total), the overload will cause them big problems next turn. If they aren't dead yet, use Life Tap to counteract their card advantage and keep on the pressure until you finish them off.
Vs Hunter
Some slower Hunter decks try to control the board with a lot of creature killing spells. Just get off to a quick start and keep the pressure up and you have the advantage.
Another type of Hunter deck is very aggressive with charge creatures and damage spells. They are dangerous and have a decent shot at killing you before you kill them. Be careful about using Life Tap if the game is almost over and another card won't change what turn you win on, but don't be shy about Life Tap in the early turns.
Vs Paladin
Slower Paladin decks will struggle because you get too big of a lead early on and you can keep up the pressure instead of running out of cards like non-Warlock aggressive decks often do. If they live to late game, you can win with Jaraxxus as long as you kept the initiative before to that point. They may have some strong late game cards, but if you make Infernals for a few turns while he's defending, you're going to win.
Vs Warrior
Other Warriors play a slower approach, possibly with the Molten Giant, Warsong Commander, and Youthful Brewmaster combination for the finishing blow. Or they may have a bunch of weapons. Either way, play your creatures and kill them. If you suspect Molten Giants, it's usually still better just to keep attacking and not care about letting them get 0 mana Molten Giants; they probably didn't draw everything they need yet to be able to kill you from high life.
Vs Druid
Other Druids play with cards like Wild Growth, Innervate, and big creatures. That's a good matchup too. You can get such a big lead early that trading inefficiently for a couple large creatures is an acceptable loss and you win anyway.
Vs Priest
Their best Mind Control targets are Sylvanas and Argent Commander. Never let them steal an Argent Commander with the Divine Shield still up. Note that if they Mind Control Argent Commander, they can attack with it immediately because it has charge.
