A Beginner's Guide to Hearthstone Mechanics
State Based Checks
Combat and Creatures
So you just got a Hearthstone beta key and you're dying to try it out before you go to bed. So you boot up the Hearthstone client and... hang on wait, why is that minion not dead? I thought that spell should have killed everything? Wait, how does this mechanic work? And what up with this Taunt creature not working?
If you're looking to get into Hearthstone, or you've sat there with one eyebrow raised looking at your screen wondering what just happened, then look no further. Let's go over some of the basic Hearthstone mechanics and how things work.
State Based Checks
The first mechanic isn't something explicitly written in the game - it's instead about how the Hearthstone game engine works. Whenever an action occurs in Hearthstone, it's important to know how the game engine prioritizes effects that happen at the same time or how things are displayed in the UI. One of the most important of these to understand is state based checks.
Whenever an action is performed (e.g. combat, playing a card, etc.) the game first performs a "check" to see if anything should trigger before the action completes. The most obvious example is how Secrets normally trigger before an attack or spell completes. Those who have played games like Magic: The Gathering will be familiar with the idea of State Based Checks. For those who are new to this mechanic, here's an example of how state based effects might lead to an non-intuitive outcome.
Acolyte of Pain
Acolyte of Pain and Cult Master are both minions that let you draw more cards when something happens to your creatures - Acolyte of Pain like to take damage while Cult Master wants the creatures you control to die. There's an important but subtle difference between the two however.
With Acolyte of Pain, you get to draw a card every time it takes damage. Intuitively, this means no matter how much damage it takes or if it kills the minion, you should draw a card every time damage is dealt. And you'd be right! When Acolyte of Pain takes enough damage to kill it and its health value drops to 0 or even negative, the game pauses for a moment and its ability triggers. That's an example of how the game performs a state based check every time combat occurs. It recognizes that once damage is dealt the Acolyte of Pain will trigger and let you draw a card before it finally resolves the combat sequence. Here, another state based check occurs and the game "sees" that Acolyte of Pain has 0 or less health so it finally dies.
Cult Master is very different however. Here, you only get to draw a card every time any of your other minions die. But what if your opponent plays an AoE spell like Flamestrike and kills your entire board in one go? Cult Master won't trigger on any of the deaths because everything dies at the same time. Thus, the state based checks won't ever get a chance for the dying and Cult Master's ability to occur at the same time. This is a big difference from the way abilities in Magic: The Gathering "see" creatures dying and is important to keep in mind!
Combat and Creatures
Combat and Creatures are two of the most important things in Hearthstone, so it's important to know all the tricks them. There's nothing worse than thinking you have the kill and then finding out you were wrong because you didn't realise how a certain mechanic worked.
For people who have played other card games such as Magic: The Gathering, this concept will be fairly simple. Whenever you play a creature from your hand, it cannot attack immediately unless it has the Charge ability. However, this also includes creates summoned by Hero Powers, creatures stolen from your opponent (such as with Mind Control) or other methods (such as resurrection effect of Redemption). That means no sneaky combat tricks with suicidal minions or stealing your opponent's minions sadly. You'll have to wait a turn, or find a way to give it Charge instead! You can tell if a minion has Summoning Sickness because there will be green "Zzzzz"s coming off it. Think of it as if the minion needs some time to rest after being summoned into your fight.
Do be aware that Shadow Word: Madness is slightly different as it allows you to attack with the creature you stole on that turn despite it not saying so on the card itself. It makes sense though as it's a one-turn steal rather than a permanent steal.
Windfury and Charge
Windfury and Charge are both abilities that modify the way a creature can attack. Windfury allows a minion to attack twice in a turn. In terms of game mechanics, it's very binary. So long as you haven't attacked twice in a turn and you aren't affected by Summoning Sickness, Windfury will allow you to keep attacking. That means that attacking with a minion, giving it Windfury, and attacking again is a completely legal play!
Charge allows a creature to ignore Summoning Sickness. When the creature gains the Charge ability is not important; so long as it has Charge you can always attack with it. It's again a completely binary mechanic just like Windfury.
A more technical way of looking at these abilities is that whenever a spell or creature is played, the game performs a State Based Check to see if a creature is allowed to attack. If a condition such as Windfury or Charge applies, then the game "overrides" certain rules such as Summoning Sickness or the "already attacked once" rules.
Battlecry is an ability that occurs when a creature is played from your hand. This means that if the creature comes into play through some other method (such as Alarm-o-Bot) the Battlecry effect does not occur. One thing that is very useful is that Battlecry effects occur before Secrets can trigger! That means if you play a Nightblade and the enemy Hunter's Snipe Secret is triggered, you'll get the Battlecry effect and deal 3 damage to your opponent before the Nightblade dies to the Snipe.
Silence is a power that removes all abilities and buffs/debuffs from a creature. So if a creature has any text on it such as a keyword (words in Bold like Charge, Windfury, Taunt, etc.) or special text (such as on a Water Elemental) all of it get removed. If a creature has any buffs that have been applied (which you can see underneath the card image when you hover your mouse over it) those are also removed.
Silence only removes the current buffs/debuffs/text on a creature. You can still apply new buffs or debuffs to a creature that's been Silenced. Returning the creature to your hand and playing it again will turn it into a complete fresh new creature too. Interestingly, Silence will remove Freeze on a minion (which might be useful when you just need one last point of damage to kill that pesky mage!).
Enrage means that creatures gain special abilities while they are damage. It's a fairly straightforward ability - if the minion's health value is in a red color, then Enrage will trigger. Just be aware that if you heal said minion and its health value turns back to a white or green color then, Enrage will stop!
Stealth and Taunt
If a creature has Stealth, then it can't be targeted by minions or spells. Do be aware however that minions can still be hit by AoE effects, such as being next to a creature targeted by Cone of Cold. However, you can also use this to your advantage. If you put a Stealth minion in between two other minions, then if your opponent tries to play that Cone of Cold they can only hit two creatures at most instead of being able to hit all three! It's also important to note that Silence will remove Stealth, although this would require an AoE spell since Stealth still negates targeted Silence spells.
Taunt creatures have to be attacked first before other creatures or players can be attacked. If your opponent has more than one Taunt creature in play, you can choose which one to attack. Taunt does not stop your opponent from Targeting spells or Hero Powers like Fireblast to hit creature behind the taunt wall however.
When a creature has both Stealth and Taunt, the Stealth takes priority. (So that means no hiding behind an untargetable wall sadly.) If the creature attacks and breaks Stealth the Taunt is kept though and will then work as normal.
Whenever you summon a creature, it has a base health value which appears in the lower right of the card. The way health values interact with combat damage, buffs, debuffs, spells and abilities can be pretty complicated. Maybe you've summoned a Bloodfen Raptor which has 2 base health and then you double its health with a spell so it now has 4 health. It takes two damage from combat. But wait, why is it's health value in red and still counts as being damaged even though its current health of 2 is the same as what it was summoned with? The Bloodfen Raptor now gets Silenced by something and... now that exact same health of 2 doesn't count as damaged any more?
The best way to describe all of these interactions is to think about health like a jug of water. Initially when the Bloodfen Raptor is first summoned the jug has a size of 2 and has 2 units of water in it. When you apply a buff, it alters the base health of the creature. The jug becomes bigger and you now have a size 4 jug with 4 units of water in it
Your Bloodfen Raptor now takes 2 damage. This is like pouring out 2 units of water from the jug. Because the jug is no longer full, the minion counts as being damaged.
Your Bloodfen Raptor is now Silenced. So the jug is magically turned back into size 2 jug. But it still has 2 units of water in it, so it's still full so the minion no longer counts as being damaged.
For those of you who have played Magic: The Gathering you'll notice that damage is no longer "remembered" by a minion whenever its health changes, which is why in this example the Bloodfen Raptor doesn't die after being Silenced despite having already taken two points of damage before. The game removes the empty part of the jug first, while still keeping the water.
It's very important to recognise how these interactions work! Let's say your opponent has a Worgen Infiltrator and a Blood Imp (a minion with 1 Base Health but gives +1 Base Health to all other friendly minions when it's in play). Here, the Worgen has 2 health (1 from its base health, and 1 from the Blood Imp Buff). If you were to play Arcane Explosion and do 1 damage to all creatures in play, you'd kill the Blood Imp but not the Worgen! That's because the Blood Imp won't die until after the damage is done and State Based Checks occur. And because damage isn't "remembered" the same way it is in Magic: The Gathering, the Worgen will still be on the board ready to hit your face next turn.
And let me tell you, it really sucks having to learn this the hard way.
There are also several other interesting interactions to be aware of.
Control and Ownership
In Hearthstone, if you control a minion you also own that minion. For example, let's say a Priest uses Mind Control and takes a King Mukla from a Hunter. The Priest is now the controller and owner of King Mukla. This is important, because if King Mukla then attacks into a Freezing Trap, it goes to the Priest's hand and not the Hunter's hand!
If you Overload, your mana next turn is locked up for that number of mana crystals regardless if you have that many mana crystals or if you obtain more from some other way. For example, let's say our Shaman player Overloads for 6 on Turn 4. On Turn 5, he only has 5 mana crystals but all of them are locked. Our Shaman now uses The Coin. However, he will still have 6 mana crystals locked. If alternatively somehow he has stolen an Innervate from a Druid player (such as from Lorewalker Cho), then he would have 1 mana crystal available.
Creature and Card limits
You can only have 7 minions on the battlefield. If you already have 7 minions on the board you can't play more. That means if your opponent is at 1 life but all your minions are frozen and you have a Charge minion in your hand, you'll have to find a way to kill one of your own minions. Of course, you can always silence a minion to remove the Freeze.
Your hand also has a maximum limit of 10 cards. If you try to draw more cards than this, you'll draw the card but then automatically discard it. (This also means you can't avoid Fatigue damage by trying to hold a full hand of cards to avoid drawing more.)
Shamans also cannot summon more than one of each totem from their Hero Power. If you already one of each in play, then your Hero Power won't work. This also includes copies of Totems you might have stolen from your opponent from some way (e.g. Sylvanas Windrunner). You also can't get cute by trying to use Brewmasters to put a Totem into your hand and then summoning a new one with your Hero Power. You'll have a copy of the Totem in your hand you can play, but you'll be forbidden from playing it.
On an interesting note, Totems from the Shaman Hero Power and Silverhand Recruits from the Paladin Hero Power have 1 mana cost, while Infernals from Lord Jaraxus' Hero Power have a mana cost of 6.
You can only play one of each Secret at any time, but there's no limit as to how many unique Secrets you have active. This does include Secrets obtained from Lorewalker Cho. As mentioned earlier, Battlecry effects will occur before Secrets trigger but the same applies for other triggered abilities. For example, a Mana Wyrm will still get +1 attack from a Spell being played even if that Spell then triggers a Counterspell Secret.
Cloning is exact
If you clone a minion (e.g. Faceless Manipulator), you copy the minion exactly as it currently is (including damage taken, buffs, etc.) and not as if you summoned it (e.g. Argent Crusader that lost Divine Shield will be a no Divine Shield Crusader).
Priests are bad at aggro
If you play the Priest card, Mindgames, but your opponent has no valid minions to copy, you only get a 0/1 minion. So you can't actually kill them with it. Interestingly, said minion has a mana cost of 0, so it's useful for triggering a Rogue Combo, if for some bizarre reason, you also have the Rogue Cards, Vanish and Headcrack, and you need two turns worth of Headcracking to win...
...But they are good at stalling
Lightwell will trigger before drawing cards. So if you're down to the wire in a Fatigue battle on an otherwise empty Board, you can stall dying to Fatigue for quite a few turns.
It's also important to note that while you can heal a minion that's already full health, it won't "recognize" the heal (e.g. for Northshire Cleric purposes).