History GameBreaker / HearthstoneHeroesOfWarcraft

* Certain unlikely card combinations can utterly break the game. Observe, what happens when you [[https://www.youtube.com/watch?v=DwaqjAfhCpI combine Mal'Ganis with Stealth, and the enemy does not have sufficient area of effect spells.]] Likewise, for the love of god, ''never'' play Millhouse Manastorm while your opponent has Archmage Antonidas on the field, because if they have a spell ''you will lose''. [[note]] Millhouse Manastorm's battlecry causes every spell in your opponent's hand to cost 0 mana the turn after he's played; this includes any new spells the opponent gains their turn. Archmage Antonidas creates a Fireball spell in your hand after you cast a spell, whether or not it was a Fireball. Do the math.[[/note]]

* Leper Gnome, a 2/1 minion for 1 mana with a Deathrattle of dealing 2 damage to the enemy hero. Unless your opponent has a Taunt minion, there is '''no''' reason for it not to just attack him/her head-on until one of their minions or they themselves take it out, either with a Hero Power, spell or a weapon. Either way, they're guaranteed to lose at least 2 health very early on.

* The Charge keyword. Any minion with Charge attached sacrifices a lot of stat points in exchange for the ability to attack immediately. It sounds fine at first, because after all a minion with Charge is no different than a damaging spell, and sometimes they're less efficient as well (compare the 3 mana 3-1 Charge Wolfrider to the 2 mana deal 3 damage Darkbomb for example). There's two key differences: Chargers are minions, meaning that the opponent has to go through the effort of removing them, meaning that aggro decks can use them to reliably go for the face because their opponent will need to use resources to kill it, leaving the aggro player with the advantage. The other, more significant problem is that Chargers can be buffed by spells and other minions. For more specific cases, here's a list:

** On their own, Force of Nature and Savage Roar are pretty reasonable cards. The former is a 6 mana spell that summons 3 2/2 Treants with Charge that die at the end of the turn, the latter is a 3 mana spell that grants all friendly characters +2 attack. ''Combined'', however, you have an absurdly powerful 14 damage, 2 card combo that is run in every single Druid deck. The main problem with the combo is that even though it's no worse than say a double Fireball from a Mage or Cruel Taskmaster+Grommash combo from Warrior, ''this'' combo actually scales with the Druid's board state, as every minion on the board adds an additional 2 damage to the combo. Adding to this, the combo is highly flexible, i.e. you can use it in case you need to kill a big minion or multiple smaller minions. Finally, there's the Double Combo, which is the previous combo with Innervate and another Savage Roar added in, bringing up the minimum damage to ''22''.
* Big game hunter is a 4/2 for 3 mana, a ho-hum minion that can get killed by something as simple as a 1-mana minion of spell. What makes this card notorious is its battlecry effect: it '''instantly kills any minion with 7 or more attack'''. It was designed to kill giants, but with the rise of doctor boom big game hunter made it in nearly every deck to counter him. It has gotten so bad that the community will [[IncrediblyLamePun shoot down]] any high cost legendary minion with 7+ attack, because it dies to BGH.

[[folder:''Whispers of the Old Gods'']]
* C'thun is an interesting case, because the minion itself is only half the reason he's so powerful. He doesn't look all that impressive at first—he's a 10-mana 6/6 that deals damage equal to his attack to enemy minions on Battlecry. The problem is that there are ''so many cards'' whose effects are solely devoted to buffing that attack up through various effects as well—so many, in fact, that it's not uncommon to see that 6/6 become a ''16/16'' once C'thun is played on turn 10—by that point, the sheer amount of damage can wipe entire fields, heroes, or even both.
** To make matters worse there is Doomcaller, and 8-mana 7/8 who not only buffs C'thun another 2/2, but say you actually managed to kill C'thun, Doomcaller puts him right back in the deck.
[[/folder]]

** On their own, Force of Nature and Savage Roar are pretty reasonable cards. The former is a 6 mana spell that summons 3 2/2 Treants with Charge that die at the end of the turn, the latter is a 3 mana spell that grants all friendly characters +2 attack. ''Combined'', however, and you have an absurdly powerful 14 damage, 2 card combo that is run in every single Druid deck. The main problem with the combo is that even though it's no worse than say a double Fireball from a Mage or Cruel Taskmaster+Grommash combo from Warrior, ''this'' combo actually scales with the Druid's board state, as every minion on the board adds an additional 2 damage to the combo. Adding to this, the combo is highly flexible, i.e. you can use it in case you need to kill a big minion or multiple smaller minions. Finally, there's the Double Combo, which is the previous combo with Innervate and another Savage Roar added in, bringing up the minimum damage to ''22''.

* In term of Hero Power, the Warlock and old Rogue Hero Power (Life Tap and Dagger Mastery) are good candidates for this. To elaborate: Gu'dan's Hero Power allows him to draw a card as a cost of 2 mana and 2 health, meaning that a well-built Warlock deck can eliminate the need for card draw, save their card slot for other card options ''and'' offers the Warlock discount for 8/8 powerhouses like Mountain Giant and Molten Giants while Valeera's old Hero Power used to be able to give her weapon +1 attack if she already had one attached instead of destroying it, allow her to maintain board control and crush many of the opponent card just by hitting and buffing her weapon. While Dagger Mastery was nerfed out of the increasing attack, Life Tap just got better with the release of better healing like Antique Healbot and Reno Jackson. Life Tap was so good that the developers only released medium class cards for Warlock our of fear of the class being overpowered

* In term of Hero Power, the Warlock and old Rogue Hero Power (Life Tap and Dagger Mastery) are good candidates for this. To elaborate: Gu'dan's Hero Power allows him to draw a card as a cost of 2 mana and 2 health, meaning that a well-built Warlock deck can eliminate the need for card draw, save their card slot for other card options ''and'' offers the Warlock discount for 8/8 powerhouses like Mountain Giant and Molten Giants while Valeera's old Hero Power used to be able to give her weapon +1 attack if she already had one attached instead of destroying it, allow her to maintain board control and crush many of the opponent card just by hitting and buffing her weapon. While Dagger Mastery was nerfed out of the increasing attack, Life Tap just got better with the release of better healing like Antique Healbot and Reno Jackson.

* In term of Hero Power, the Warlock and old Rogue Hero Power (Life Tap and Dagger Mastery) are good candidates for this. To elaborate: Gu'dan's Hero Power allows him to draw a card as a cost of 2 mana and 2 health, meaning that a well-built Warlock deck can eliminate the need for card draw and save their card slot for other card options and offers the Warlock discount for 8/8 powerhouses like Mountain Giant and Molten Giants while Valeera's old Hero Power used to be able to give her weapon +1 attack if she already had one attached instead of destroying it, allow her to maintain board control and crush many of the opponent card just by hitting and buffing her weapon. While Dagger Mastery was nerfed out of the increasing attack, Life Tap just got better with the release of better healing like Antique Healbot and Reno Jackson.

** The Void Terror truly lives up to its name if you manage to feed Stalagg and Feugen to it simultaneously. Because of the way deathrattles trigger, both minions die first and the game ''then'' checks if either Stalagg or Feugen is dead for the deathrattle to go off. Since they're both dead, both their deathrattles also trigger, which means [[OhCrap that you summon two 11/11 Thaddeuses at once.]] Have Rivendare on the board? [[NoKillLikeOverkill That's four Thaddeuses.]] Oh, and don't forget about that Void Terror - it's now, at best, a 14/14 monstrosity. Unless your opponent has gotten really lucky with hard removal or is packing a complete board clear (such as Twisting Nether, which is seldom used) they're very probably very dead.

* Piloted Shredder is the most used neutral card in the game and one of the most efficient as well. As a 4/3 for 4 mana that summons a 2-cost minion when it dies, it has just enough attack to kill almost all minions that cost the same or less than it while leaving a body behind, which can be used to finish off anything that survived the first hit. With this in mind, there is practically no other 4 mana minions worth using as there is ''nothing'' that can straight up beat Piloted Shredder, they can only trade with it at best or accomplish nothing and die at worst, with only utility minions like Water Elemental getting any free passes. This is without getting into the deathrattle itself, which has the chance to spawn overstatted minions like Millhouse Manastorm. The only downside to using it is the possibility it might spawn Darnassus Aspirant or Doomsayer, but considering how often it hits compared to how often it misses, who cares?

* The Charge keyword. Any minion with Charge attached sacrifices a lot of stat points in exchange for the ability to attack immediately. It sounds fine at first, because after all a minion with Charge is no different than a damaging spell, and sometimes they're less efficient as well (compare the 3 mana 3-1 Charge Wolfrider to the 2 mana deal 3 damage Darkbomb for example). There's two key differences: Chargers are minions, meaning that the opponent has to go through the effort of removing them, meaning that aggro decks can use them to reliably go for the face because there opponent will need to use resources to kill it, leaving the aggro player with the advantage. The other, more significant problem is that Chargers can be buffed by spells and other minions. For more specific cases, here's a list:

** Leeroy Jenkins used to be 6/2 for 4 mana that summoned 2 1/1 Whelps for his opponent. On top of the downside straight up ''not mattering'' if he is used to end the game, his damage to mana ratio is equivalent to Fireball, one of the most efficient damage spells in the game. This is without getting into his status as the win condition of Miracle Rogue, which was the reason he had to be nerfed in the first place. Basically, after a Miracle Rogue was done drawing all their cards with Gadgetzan Auctioneer, they would summon Leeroy, attack, and then bring him back to their hand with Shadowstep, not only allowing them to use him again but it decreases his cost by 2, meaning that there was still mana leftover to do whatever they wanted. It wasn't just Miracle Rogue that ran him though- Combo Warlocks, Druids, Aggro Hunters, most decks ran Leeroy even if they couldn't use him to his full potential because he was ''just that freaking good''. He was later nerfed to 5 mana, which severely reduced his usage.

* Dr. Boom is a 7/7 for 7 mana that summons 2 1/1 Boom Bots into battle with him, with the both of them having the deathrattle of dealing 1-4 damage to a random enemy. Because of how many bodies he brings to the board, very few cards can completely deal with Dr. Boom by themselves, requiring inadequately used resources just to get rid of him. Additionally, because he costs 7, he can be reliably played in almost any game, to the point where even aggressive decks can use him.

** Murloc Knight is the main reason for Paladin's popularity in Arena. It's a 3/4 for 4 with the inspire effect of summoning a random murloc. In constructed, it's ''the'' most popular inspire minion because of its potential to summon something scary like Murloc Warleader, Old Murk-Eye, or another Murloc Knight, mainly held back by its overcrowded mana slot and high potential to whiff. In Arena, removal is much more sparse, meaning that Murloc Knight will likely stick around long enough to pop multiple times, almost assuring board control in a game mode ''defined'' by board control. It got so bad Blizzard directly introduced two lowly statted murlocs in ''League of Explorers'' just to nerf it.

** Kel'Thuzad was insane for the longest time. In constructed, having a developed board either means you're playing an aggro deck or you were already winning, meaning Kel'Thuzad usually only sees play in Druid decks, which can reliably have a big minion on the board prepared for him to resurrect, and deathrattle Shaman which is focused on duplicating him with Reincarnate. Arena is different; both sides will almost always have some minions in play with complete resets being rare, a situation which is utterly pristine for card based around having a board. Indeed, dropping Kel'Thuzad was a death sentence for the opponent, as the astronomical board advantage meant that not even the ever feared Flamestrike could stop him. He got much worse as Arena became faster with the addition of more cheap minions, but even still most people will take Kel'Thuzad the second he shows up.

* Leper Gnome, a 2/1 minion for 1 mana with a Deathrattle of dealing 2 damage to the enemy hero. Unless your opponent has a Taunt minion, there is '''no''' reason for it not to just attack him/her head-on until one of their minions or they themselves take it out, either with a Hero Power, spell or a weapon. Either way, they're guaranteed to lose at least 2 health very early on.

* Leper Gnome, a 2/1 minion for 1 mana with a Deathrattle of dealing 2 damage to the enemy hero. Unless your opponent has a Taunt minion, there is '''no''' reason for it not to just attack him/her head-on until one of their minions or they themselves take it out, either with a Hero Power, spell or a weapon.

* Leper Gnome, a 2/1 minion for 1 mana with a Deathrattle of dealing 2 damage to the enemy hero. Unless your opponent has a Taunt minion, there is '''no''' reason for it not to just attack him/her head-on until one of their minions or they themselves take it out, either with a Hero Power or with a weapon.

* From the vanilla game:
** Two Divine Spirits [[note]]A spell that doubles a minion's Health[[/note]] used on a decently sized minion will give that minion a very high health pool, and casting Inner Fire on it [[note]]Change a minion's Attack to be equal to its Health[[/note]] gives the opponent a problem that hits as hard as it can take. HuskyStarcraft and his friend Sinvicta discovered that, if you use Lorewalker Cho [[note]]which puts a copy of any spell used into the other player's hand[[/note]] and can get your opponent to co-operate with you, you can very easily get a Minion up above [[http://www.youtube.com/watch?v=SOD7Ni_3NIc 1 billion health]]. However, as the game moved on, the strategy became considered too gimmicky to be viable due to the amount of setup required to pull it off.
** The Mage's Pyroblast spell was seen as this early in the game's life. The card deals 10 damage to a single target on the field, the opposing hero included. That means that if a player ever fights a Mage and goes under 10 health, the game might very well be over after their next turn, because there's nothing you can do to stop the Pyroblast besides healing yourself (Relatively rare possibility outside of Priest) or a specific Mage secret that "counters" an opponent's spell and stops it from casting. Its mana cost was increased from 8 to 10 as a result and the card essentially died along with Mage as other classes became popular and found new decks that worked well against Mage.
** The Priest's Mind Control [[note]]Take control any an enemy minion[[/note]] spell. If a match goes past Turn 10, very likely considering how much Priest's card set can slow the game down, then any of your high-Mana and high-value minions can be stolen by a Priest up to twice. This was even worse before when it was '''8''' mana instead of 10.
** The Twilight Drake was a 4 mana 1/1 creature that had a battlecry of gaining +1/+1 for every card in the player's hand when it was played. If the enemy didn't have silence to deal with it instantly, then they had, at minimum, a 6/6 running around rampant on turn 4, something that required a disproportionate amount of effort to kill compared to its ease of summoning. Worse yet, they weren't legendary, meaning there could be 2 in the deck. It was later nerfed to be a 4 attack and 1 health minion that gains +1 health for every card in the hand at time of it being summoned, making it a solid card but much more manageable.
** Flamestrike. It's one of the Basic cards, so everyone has one. Yet it is ''the'' single most feared [[HerdHittingAttack Board Clear]] in a Mage's arsenal, and it is not an exaggeration to say that entire match can, and has been turned around simply from a single cast of this spell. The typical advice for playing against Mage when the game goes late is to make your board good enough to bait out their first Flamestrike (That you must ''always'' assume they have by Turn 7) but without using your really good cards.
** Warrior used to have some ''stupid'' OTK combos, but the most infamous is an incredibly simple 3 card combo involving Alexstrasza, Charge, and Gorehowl. All the warrior had to do was stall the game until they could play Gorehowl on one turn, then play Alexstrasza on the next turn by setting the opponent's health to 15, then give her Charge. Assuming there are no taunts in the way, Gorehowl's 7 damage plus Alex's 8 damage amounted to exact, easy lethal. The combo was so broken, Charge got ''massively'' nerfed from a 0 cost spell to a 3 cost spell.
** Savannah Highmane, a 6/5 hunter minion for 6 mana that spawns 2 2/2 Hyenas when it dies. Because of how sticky it is, a hunter can just reliably go for the enemy hero's face instead of trading, and the nasty body ensures that their opponent will need to deal with it. Combined with the hunter's naturally high amount of direct damage cards, and you have a minion that can ensure victory just by hitting the enemy hero ''once''.
** The vanilla game had a pretty bad problem with card draw engines. Basically, if any card could theoretically draw a massive amount of cards, players would figure out ways to abuse it so that they can. Starving Buzzard and Gadgetzan Auctioneer were pivotal pieces of Combo Hunter and Miracle Rogue respectively and threatened to end the game by themselves before they got nerfed to the ground, and arguably the main reason the Patron Warrior deck is so strong is because Battle Rage can consistently draw a large amount of cards for a piddly 2 mana. Acolyte of Pain, Coldlight Oracle, Cult Master, and Divine Favor are similarly abused, but they're nowhere near as bad as the other three.
* From ''Naxxramas'':
** Undertaker used to be a 1/2 for 1 mana that gained +1/+1 every time a friendly minion with deathrattle was summoned. It was widely abused by the Hunter class in its days because of how damn ''fast'' it could get out of control, from turn 1 even, and the sheer speed of Hunter decks in general meant that gaining back the lead was very difficult. It was later nerfed so that it no longer gained health, and was never played again, to the joy of players.
** Mad Scientist is a 2/2 minion for 2 mana with the deathrattle of putting a secret from the owner's deck into the battlefield. Drawing a specific type of card is completely nonexistent aside from the Sense Demons spell, so a card that not only does that but puts it into play without needing to pay for it is obscene, all for a measly 2 mana, attached to a 2/2 creature to boot.
** Voidcaller, a 3/4 minion for 4 mana with the deathrattle of putting a demon from your hand into the field. Not only can it replace itself the second it dies, but it can summon demons with a ''higher'' cost than itself, including Doomguard, Dread Infernal, and the almighty Mal'Ganis. Even if you don't have a demon in your hand, ''your opponent has no way of knowing'', meaning that they have to play ridiculously safely or come up with a backup plan to deal with whatever comes out of it, or use one of their very few silences on it.
* From ''Goblins vs. Gnomes'':
** Dr. Boom is a 7/7 for 7 mana that summons 2 1/1 Boom Bots into battle with him, with the both of them having the deathrattle of dealing 1-4 damage to a random enemy. Because of how many bodies he brings to the board, very few cards can completely deal with Dr. Boom by themselves, requiring inadequately used resources just to get rid of him. Additionally, because he costs 7, he can be reliably played in almost any game, to the point where even aggressive decks can use him.
** Mechwarper is a 2/3 for 2 mana that reduces the cost of all mechs in your hand by 1, and is the backbone of basically every mech deck. On top of allowing the player to basically vomit out their hand it also decreases the cost of the other Mechwarper, reducing the cost of all mechs 2 instead of 1, allowing for further vomiting.
** Piloted Shredder is the most used neutral card in the game and one of the most efficient as well. As a 4/3 for 4 mana that summons a 2-cost minion when it dies, it has just enough attack to kill almost all minions that cost the same or less than it while leaving a body behind, which can be used to finish off anything that survived the first hit. With this in mind, there is practically no other 4 mana minions worth using as there is ''nothing'' that can straight up beat Piloted Shredder, they can only trade with it at best or accomplish nothing and die at worst, with only utility minions like Water Elemental getting any free passes. This is without getting into the deathrattle itself, which has the chance to spawn overstatted minions like Millhouse Manastorm. The only downside to using it is the possibility it might spawn Darnassus Aspirant or Doomsayer, but considering how often it hits compared to how often it misses, who cares?
** Unstable Portal, which is the leading candidate for the most hated card in ''Hearthstone''. It's a 2 mana Mage spell that adds a random minion to the owner's hand and reduces its cost by 3. It's a cheap, non-reactive spell, meaning you can play it any time you want, and it has synergy with the majority of a Mage's arsenal such as Mana Wyrm, Flamewaker, and Archmage Antonidas. That's before getting into the effect itself, which is randomness gone ''horribly wrong''; as many pro players have noted, Unstable Portal's main strength is that even if it whiffs you still don't lose the game, while most other times it will end the game by itself. There's no downside to it. Even if you get a Wisp instead of Ragnaros, a Wisp is still a minion you can put on the board, while most other times you'll get something insane like a 5-cost Tirion Fordring or a 3-cost Boulderfist Ogre. Even terrible cards like War Golem aren't that bad if it gets played on ''turn 4''.
* From ''Blackrock Mountain'':
** Emperor Thaurissan. He's a 5/5 for 6 with the ''utterly godlike'' ability to reduce the cost of all cards in his owner's hand at the end of each turn. In control decks, he's good because he can reduce the cost of the big lategame minions so that they can be played earlier and more frequently, but it's nothing too terrible until he gets put into a combo deck. Thaurissan alone singlehandedly created loads of overtly strong combo decks, most infamously Patron Warrior, while bolstering those that already existed, as the nature of his ability meant that not only could the game winning combos be done ''earlier'' but they could made even stronger. To give an idea of how much impact he had, full 30 damage one turn kills became ''the norm'' instead of a once in a blue moon sort of thing.
* From ''The Grand Tournament'':
** Nozdormu's [[GameBreakingBug brain-breaking glitchyness]] came in full force with the addition of Joust. See, whenever the "end turn" button is pressed, the animation times from the previous turn carry over into the next turn, directly affecting the amount of time a player can take on their turn. This oversight is usually exploited by playing Nozdormu, who reduces the time each player has during their turn to 15 seconds, and then playing as many overtly long animations as possible to skip their opponent's turn. Beforehand, it required a convoluted set-up and wound up being to gimmicky to be consistent. Joust cards brought this problem to the forefront; the animation that plays whenever a Joust is activated is extremely long, to the point where simply playing ''1'' Joust in conjunction the Nozdormu exploit was enough to skip the opponent's turn. Suddenly it became a problem, as the Nozdormu player simply had to get the bronze dragon and a single jouster in his hand to ''win the game''. Thankfully, while Nozdormu is still infamously broken his interaction with Joust cards was patched within a day, though the previously mentioned gimmick set-up still exists.
** Mysterious Challenger, a 6/6 for 6 mana Paladin minion that puts up to 5 secrets from your deck into the battlefield for free. Paladin secrets were notoriously crappy prior to his appearance, and the intended downside to Challenger was that in order to maximize his value you had to put some ''real'' terrible cards into your deck. While these are both real issues that spring up in Challenger decks, it turns out they don't matter that much, because by specifically building the deck with the secrets in mind, you can secure board control and force the opponent to make sub optimal plays just to get it back. This is all without getting into when Mysterious Challenger himself hits the field on turn 6, which is far and away one of the most powerful ''things'' in the game. On average, he pulls Avenge, Noble Sacrifice, Repentance, Competitive Spirit, and Redemption from the deck, which means his owner will no longer have to worry about drawing any of them and giving them better odds of drawing their late game cards, like Tirion or another Challenger. Killing him is a nightmare, because the combination of secrets makes it so that if you kill him with spells, he comes back with 1 health while trying to kill him with an attack will negate the attack and give him +3/+2. Simply put, it's not for nothing that his deck is the one that plagued the ladder more than any other deck in the game's run.
* From ''League of Explorers'':
** Reno Jackson, a 6 mana 4/6 that will fully restore your hero's life as long as you don't have any duplicate cards, will break the will of any player going up against his specialized deck. Basically you let the opponent waste cards and life going against your random minions and just when they think they have you, usually when your life is less then ten, you throw out Reno and watch your opponent despair at the thought of grinding you down again with a lot less cards. For maximum despair play a Brewmaster or another card that allows you to put Reno back in your hand, its enough to make your opponent quit. Of course this is assuming all goes well and depends a lot on drawing a good curve, as well as not letting your opponent have any good cards by the time you play Reno.

* GameBreaker:
** From the vanilla game:
*** Two Divine Spirits [[note]]A spell that doubles a minion's Health[[/note]] used on a decently sized minion will give that minion a very high health pool, and casting Inner Fire on it [[note]]Change a minion's Attack to be equal to its Health[[/note]] gives the opponent a problem that hits as hard as it can take. HuskyStarcraft and his friend Sinvicta discovered that, if you use Lorewalker Cho [[note]]which puts a copy of any spell used into the other player's hand[[/note]] and can get your opponent to co-operate with you, you can very easily get a Minion up above [[http://www.youtube.com/watch?v=SOD7Ni_3NIc 1 billion health]]. However, as the game moved on, the strategy became considered too gimmicky to be viable due to the amount of setup required to pull it off.
*** The Mage's Pyroblast spell was seen as this early in the game's life. The card deals 10 damage to a single target on the field, the opposing hero included. That means that if a player ever fights a Mage and goes under 10 health, the game might very well be over after their next turn, because there's nothing you can do to stop the Pyroblast besides healing yourself (Relatively rare possibility outside of Priest) or a specific Mage secret that "counters" an opponent's spell and stops it from casting. Its mana cost was increased from 8 to 10 as a result and the card essentially died along with Mage as other classes became popular and found new decks that worked well against Mage.
*** The Priest's Mind Control [[note]]Take control any an enemy minion[[/note]] spell. If a match goes past Turn 10, very likely considering how much Priest's card set can slow the game down, then any of your high-Mana and high-value minions can be stolen by a Priest up to twice. This was even worse before when it was '''8''' mana instead of 10.
*** The Twilight Drake was a 4 mana 1/1 creature that had a battlecry of gaining +1/+1 for every card in the player's hand when it was played. If the enemy didn't have silence to deal with it instantly, then they had, at minimum, a 6/6 running around rampant on turn 4, something that required a disproportionate amount of effort to kill compared to its ease of summoning. Worse yet, they weren't legendary, meaning there could be 2 in the deck. It was later nerfed to be a 4 attack and 1 health minion that gains +1 health for every card in the hand at time of it being summoned, making it a solid card but much more manageable.
*** Flamestrike. It's one of the Basic cards, so everyone has one. Yet it is ''the'' single most feared [[HerdHittingAttack Board Clear]] in a Mage's arsenal, and it is not an exaggeration to say that entire match can, and has been turned around simply from a single cast of this spell. The typical advice for playing against Mage when the game goes late is to make your board good enough to bait out their first Flamestrike (That you must ''always'' assume they have by Turn 7) but without using your really good cards.
*** Warrior used to have some ''stupid'' OTK combos, but the most infamous is an incredibly simple 3 card combo involving Alexstrasza, Charge, and Gorehowl. All the warrior had to do was stall the game until they could play Gorehowl on one turn, then play Alexstrasza on the next turn by setting the opponent's health to 15, then give her Charge. Assuming there are no taunts in the way, Gorehowl's 7 damage plus Alex's 8 damage amounted to exact, easy lethal. The combo was so broken, Charge got ''massively'' nerfed from a 0 cost spell to a 3 cost spell.
*** Savannah Highmane, a 6/5 hunter minion for 6 mana that spawns 2 2/2 Hyenas when it dies. Because of how sticky it is, a hunter can just reliably go for the enemy hero's face instead of trading, and the nasty body ensures that their opponent will need to deal with it. Combined with the hunter's naturally high amount of direct damage cards, and you have a minion that can ensure victory just by hitting the enemy hero ''once''.
*** The vanilla game had a pretty bad problem with card draw engines. Basically, if any card could theoretically draw a massive amount of cards, players would figure out ways to abuse it so that they can. Starving Buzzard and Gadgetzan Auctioneer were pivotal pieces of Combo Hunter and Miracle Rogue respectively and threatened to end the game by themselves before they got nerfed to the ground, and arguably the main reason the Patron Warrior deck is so strong is because Battle Rage can consistently draw a large amount of cards for a piddly 2 mana. Acolyte of Pain, Coldlight Oracle, Cult Master, and Divine Favor are similarly abused, but they're nowhere near as bad as the other three.
** From ''Naxxramas'':
*** Undertaker used to be a 1/2 for 1 mana that gained +1/+1 every time a friendly minion with deathrattle was summoned. It was widely abused by the Hunter class in its days because of how damn ''fast'' it could get out of control, from turn 1 even, and the sheer speed of Hunter decks in general meant that gaining back the lead was very difficult. It was later nerfed so that it no longer gained health, and was never played again, to the joy of players.
*** Mad Scientist is a 2/2 minion for 2 mana with the deathrattle of putting a secret from the owner's deck into the battlefield. Drawing a specific type of card is completely nonexistent aside from the Sense Demons spell, so a card that not only does that but puts it into play without needing to pay for it is obscene, all for a measly 2 mana, attached to a 2/2 creature to boot.
*** Voidcaller, a 3/4 minion for 4 mana with the deathrattle of putting a demon from your hand into the field. Not only can it replace itself the second it dies, but it can summon demons with a ''higher'' cost than itself, including Doomguard, Dread Infernal, and the almighty Mal'Ganis. Even if you don't have a demon in your hand, ''your opponent has no way of knowing'', meaning that they have to play ridiculously safely or come up with a backup plan to deal with whatever comes out of it, or use one of their very few silences on it.
** From ''Goblins vs. Gnomes'':
*** Dr. Boom is a 7/7 for 7 mana that summons 2 1/1 Boom Bots into battle with him, with the both of them having the deathrattle of dealing 1-4 damage to a random enemy. Because of how many bodies he brings to the board, very few cards can completely deal with Dr. Boom by themselves, requiring inadequately used resources just to get rid of him. Additionally, because he costs 7, he can be reliably played in almost any game, to the point where even aggressive decks can use him.
*** Mechwarper is a 2/3 for 2 mana that reduces the cost of all mechs in your hand by 1, and is the backbone of basically every mech deck. On top of allowing the player to basically vomit out their hand it also decreases the cost of the other Mechwarper, reducing the cost of all mechs 2 instead of 1, allowing for further vomiting.
*** Piloted Shredder is the most used neutral card in the game and one of the most efficient as well. As a 4/3 for 4 mana that summons a 2-cost minion when it dies, it has just enough attack to kill almost all minions that cost the same or less than it while leaving a body behind, which can be used to finish off anything that survived the first hit. With this in mind, there is practically no other 4 mana minions worth using as there is ''nothing'' that can straight up beat Piloted Shredder, they can only trade with it at best or accomplish nothing and die at worst, with only utility minions like Water Elemental getting any free passes. This is without getting into the deathrattle itself, which has the chance to spawn overstatted minions like Millhouse Manastorm. The only downside to using it is the possibility it might spawn Darnassus Aspirant or Doomsayer, but considering how often it hits compared to how often it misses, who cares?
*** Unstable Portal, which is the leading candidate for the most hated card in ''Hearthstone''. It's a 2 mana Mage spell that adds a random minion to the owner's hand and reduces its cost by 3. It's a cheap, non-reactive spell, meaning you can play it any time you want, and it has synergy with the majority of a Mage's arsenal such as Mana Wyrm, Flamewaker, and Archmage Antonidas. That's before getting into the effect itself, which is randomness gone ''horribly wrong''; as many pro players have noted, Unstable Portal's main strength is that even if it whiffs you still don't lose the game, while most other times it will end the game by itself. There's no downside to it. Even if you get a Wisp instead of Ragnaros, a Wisp is still a minion you can put on the board, while most other times you'll get something insane like a 5-cost Tirion Fordring or a 3-cost Boulderfist Ogre. Even terrible cards like War Golem aren't that bad if it gets played on ''turn 4''.
** From ''Blackrock Mountain'':
*** Emperor Thaurissan. He's a 5/5 for 6 with the ''utterly godlike'' ability to reduce the cost of all cards in his owner's hand at the end of each turn. In control decks, he's good because he can reduce the cost of the big lategame minions so that they can be played earlier and more frequently, but it's nothing too terrible until he gets put into a combo deck. Thaurissan alone singlehandedly created loads of overtly strong combo decks, most infamously Patron Warrior, while bolstering those that already existed, as the nature of his ability meant that not only could the game winning combos be done ''earlier'' but they could made even stronger. To give an idea of how much impact he had, full 30 damage one turn kills became ''the norm'' instead of a once in a blue moon sort of thing.
** From ''The Grand Tournament'':
*** Nozdormu's [[GameBreakingBug brain-breaking glitchyness]] came in full force with the addition of Joust. See, whenever the "end turn" button is pressed, the animation times from the previous turn carry over into the next turn, directly affecting the amount of time a player can take on their turn. This oversight is usually exploited by playing Nozdormu, who reduces the time each player has during their turn to 15 seconds, and then playing as many overtly long animations as possible to skip their opponent's turn. Beforehand, it required a convoluted set-up and wound up being to gimmicky to be consistent. Joust cards brought this problem to the forefront; the animation that plays whenever a Joust is activated is extremely long, to the point where simply playing ''1'' Joust in conjunction the Nozdormu exploit was enough to skip the opponent's turn. Suddenly it became a problem, as the Nozdormu player simply had to get the bronze dragon and a single jouster in his hand to ''win the game''. Thankfully, while Nozdormu is still infamously broken his interaction with Joust cards was patched within a day, though the previously mentioned gimmick set-up still exists.
*** Mysterious Challenger, a 6/6 for 6 mana Paladin minion that puts up to 5 secrets from your deck into the battlefield for free. Paladin secrets were notoriously crappy prior to his appearance, and the intended downside to Challenger was that in order to maximize his value you had to put some ''real'' terrible cards into your deck. While these are both real issues that spring up in Challenger decks, it turns out they don't matter that much, because by specifically building the deck with the secrets in mind, you can secure board control and force the opponent to make sub optimal plays just to get it back. This is all without getting into when Mysterious Challenger himself hits the field on turn 6, which is far and away one of the most powerful ''things'' in the game. On average, he pulls Avenge, Noble Sacrifice, Repentance, Competitive Spirit, and Redemption from the deck, which means his owner will no longer have to worry about drawing any of them and giving them better odds of drawing their late game cards, like Tirion or another Challenger. Killing him is a nightmare, because the combination of secrets makes it so that if you kill him with spells, he comes back with 1 health while trying to kill him with an attack will negate the attack and give him +3/+2. Simply put, it's not for nothing that his deck is the one that plagued the ladder more than any other deck in the game's run.
** From ''League of Explorers'':
*** Reno Jackson, a 6 mana 4/6 that will fully restore your hero's life as long as you don't have any duplicate cards, will break the will of any player going up against his specialized deck. Basically you let the opponent waste cards and life going against your random minions and just when they think they have you, usually when your life is less then ten, you throw out Reno and watch your opponent despair at the thought of grinding you down again with a lot less cards. For maximum despair play a Brewmaster or another card that allows you to put Reno back in your hand, its enough to make your opponent quit. Of course this is assuming all goes well and depends a lot on drawing a good curve, as well as not letting your opponent have any good cards by the time you play Reno.
** Arena has some too, but as expansions are added to the game they become less cosmically destructive, not because they're getting nerfed or anything but because more cards means a wider card pool for the draft to pick from. As time goes on, expect to see these less and less.
*** Flamestrike again, but for reasons on top of the ridiculous value it already provides. It's a common, meaning that it's very unlikely for someone to go through a Mage draft without seeing it, and the nature of Arena (trading minions and focusing on value and tempo) means that it's almost impossible not to get good use out of it. More importantly, it's possible to have more than two, meaning that with a good draft you'll have free area damage on tap prepared to eliminate anything in your way.
*** Kel'Thuzad was insane for the longest time. In constructed, having a developed board either means you're playing an aggro deck or you were already winning, meaning Kel'Thuzad usually only sees play in Druid decks, which can reliably have a big minion on the board prepared for him to resurrect, and deathrattle Shaman which is focused on duplicating him with Reincarnate. Arena is different; both sides will almost always have some minions in play with complete resets being rare, a situation which is utterly pristine for card based around having a board. Indeed, dropping Kel'Thuzad was a death sentence for the opponent, as the astronomical board advantage meant that not even the ever feared Flamestrike could stop him. He got much worse as Arena became faster with the addition of more cheap minions, but even still most people will take Kel'Thuzad the second he shows up.
** Certain unlikely card combinations can utterly break the game. Observe, what happens when you [[https://www.youtube.com/watch?v=DwaqjAfhCpI combine Mal'Ganis with Stealth, and the enemy does not have sufficient area of effect spells.]] Likewise, for the love of god, ''never'' play Millhouse Manastorm while your opponent has Archmage Antonidas on the field, because if they have a spell ''you will lose''. [[note]] Millhouse Manastorm's battlecry causes every spell in your opponent's hand to cost 0 mana the turn after he's played; this includes any new spells the opponent gains their turn. Archmage Antonidas creates a Fireball spell in your hand after you cast a spell, whether or not it was a Fireball. Do the math.[[/note]]