Game Breaker / Hearthstone: Heroes of Warcraft

"Leeroy Jenkins created a strategy that revolved around trying to defeat your opponent in one turn without requiring any cards on the board. Fighting for board control and battles between minions make an overall game of Hearthstone more fun and compelling, but taking 20+ damage in one turn is not particularly fun or interactive."

Balance is a bit of touchy issue in Hearthstone. On average you'll have one guy hollering for nerfs on, say, Harvest Golem and the next guy will be explaining why that would be a terrible idea. The stuff on this page, on the other hand? These are broken. These cards have, at one point or another, forced the meta to adapt to it significantly like no card should be allowed to, to much derision.
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    General 
  • Hero Powers:
    • In the beta, what shot Valeera up the tier list was not her combos or damage output, but her hero power. Dagger Mastery, nowadays, simply equips the hero with a 1/2 dagger. This is quite good on its own, as Rogue has a plethora of weapon boosting cards that can lead to some major face-stompage. However, Dagger Mastery had an additional bonus in the beta that made it too good; if you already had a weapon equipped, it could give the weapon an extra point of attack. Suddenly, the hero power alone can kill almost any 1 or 2 drop, making it nearly impossible to keep up with the Rogue. It didn't take long for this bonus to be removed, and the next time they tried to incorporate it with the card Poisoned Blade during The Grand Tournament, they deliberately overcosted it so that nothing stupid could come out of it.
    • Life Tap, the Warlock hero power, allows him to draw a card at 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 slots for other card options and offers the Warlock discounts for 8/8 powerhouses like Mountain Giant and Molten Giant. Notably, whereas most of the exploitable stuff in Hearthstone gains a counter or ends up nerfed, Life Tap simply got better over time with the release of better healing cards like Antique Healbot and Reno Jackson. Life Tap is so good that many fans speculate this is why the developers only release subpar class cards for Warlock out of fear of Gul'dan becoming overpowered.
  • 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, allowing for some crazy high-damage combos. Blizzard themselves have admitted that they underestimated the power of Charge, and since launch have done a much better job of balancing the mechanic.
  • Silence, a very rare card mechanic that removes all text and buffs from a minion. Silence's goal was true and noble, being intended to prevent other, much more dangerous cards like the later mentioned Tirion Fordring and Savannah Highmane from tearing the game apart, but unfortunately that didn't work out. In practice, Silence neutralized a significant chunk of the game's cards, including ones with unique mechanics that never saw the light of day because of it, and was ruthlessly abused to push Taunt minions out of the way to get a previously prevented lethal. It was so annoying that when the Whispers of the Old Gods nerfs came around, it targeted the two main Silence cards, Ironbeak Owl and Keeper of the Grove, with extreme prejudice.
  • "Curvestone", a derogatory term for a deck strategy based around simply dropping the most cost-efficient minion each turn and outvaluing the enemy until they die. The main reason why it's so good is that it gives the first turn player a giant advantage, because the second turn player is forced to be the reactive one if they don't want to lose, while Control decks simply lack enough removal to handle all of the threats. Dragons are the biggest offender of this, as some of their best cards double as removal (Blackwing Corrupter and Book Wyrm, specifically), so they don't have to give up their lead to deal with the opponents monsters. The reason why Secret Paladin dominated the game for so long is because their minions were both strong and sticky, meaning they almost never lost the board until their lategame cards hit the board and sealed the deal.
  • High damage combos are much stronger here than in other card games. Hearthstone offers no way to play the game during your opponent's turn outside of Secrets, meaning that combos can be done uninterrupted to win the game right there. Additionally, up until Dirty Rat was added in Mean Streets of Gadgetzan, there were no cards that could discard your opponent' cards, meaning they had nothing to fear before the combo dropped. Miracle Rogue, Freeze Mage and Patron Warrior were the classic examples, the first being able to draw their entire deck by around turn 5 then constantly drop insanely big minions and high damage-dealing spells to close out the game while the latter two being very stally and slow decks that wait until the combo comes together to end the game on the spot with no hope of shutting it down. Midrange Druid was a comparatively proactive deck that could easily win without their 14 damage combo.

    Nerfed/Standard-Banned Cards 
By definition, any card that has ever been nerfed or put into the Hall of Fame was probably too strong for its own good. If you need a benchmark to compare the power of certain cards, look here.

Hall of Fame

  • Old Murk-Eye is a 4 mana 2/4 Murloc with Charge that gains +1 attack for every friendly Murloc. It was mostly just a neat finisher for Murloc decks right up until League of Explorers brought Anyfin Can Happen into the game, a 10 mana Paladin spell that summons up to 7 friendly Murlocs that died that game. Murk-Eye offered two major things to the resultant Anyfin Paladin deck: a decent midgame minion that can remove some weeny minions and a devastating combo piece that can finish the job when working together with Bluegill Warriors and Murloc Warleaders. For dramatically increasing the consistency of an already consistent deck, Murk-Eye was completely banned from Standard and for Team 5 to save face they took the rest of the Reward set with him.
  • Azure Drake is a 5 mana 4/4 Dragon with Spell Damage +1 and draws a card upon summoning. It's a perennial favorite for game design enthusiasts among the fanbase due its simplicity, power, and inability to make someone rage, but a major issue many overlook is its versatility. Azure Drake essentially won the lottery with its effect variety: it's a Dragon, meaning it's good in Dragon decks by default, it has barely enough attack to be threatening (while dodging both of Priest's Shadow Word removal spells) and enough health to dodge a handful of removal, the extra spell damage is deceptively valuable, is uncontested in its mana slot, and it has one of the most undercosted card draw effects in the game. The Drake is well liked for the most part, but to assure long-term health for the game, it was booted out of Standard in 2017.
  • Sylvanas Windrunner is a 6 mana 5/5 who takes control of a random enemy minion on death. By a mile, the single best Deathrattle minion in the whole game; there's almost nothing that can beat Sylvanas in a fight and survive except for minions who summon other minions to be stolen like Onyxia or Dr. Boom. Even scarier, she simply got better over time with the addition of Deathrattle synergy cards like Unearthed Raptor and N'Zoth. To open more design space for Deathrattle synergy and overall more variety in the 6-cost slot, Sylvanas was kicked out of Standard with the Year of the Mammoth.
    • Notably, she was even better in the beta, where she costed 5 mana instead. A Warrior who uses Sylvanas in conjunction with Brawl would destroy all enemy minions and leave one for himself.
  • Ragnaros, the Firelord is an 8 mana 8/8 who can't attack, but deals 8 damage to a random target at the end of his owner's turn. He's the most iconic card in the game, stemming from his improbably high use-rate for such an expensive minion. Big minions in Hearthstone are typically weak due to the power of hard removal, meaning they either need to do something before getting removed or be annoying to remove in the first place. Ragnaros is the first requirement personified; he almost always either destroys something upon coming down or knocks off a quarter of the opponent's health, and if he sticks around he remains devastating because he never takes any damage from combat because technically he never attacks anything. Additionally, the RNG factor of Ragnaros can indirectly work in his user's favor, because a lucky coin flip can cause your opponent to get frustrated and start making mistakes. Eventually, Rag's power got him removed from Standard come the Year of the Mammoth, simply for outclassing all other lategame drops.
  • Power Overwhelming is a 1 mana Warlock spell that gives a friendly minion +4/+4, but also dies horribly at the end of the turn. What started out written off as a goofy risk-and-reward card turned out to be a devastating combo card when used together with way too many cards to count. It's most famous use is the OTK combo with Faceless Manipulator; use two Power Overwhelmings on a Charge minion, copy it with Faceless, and attack for game. After all, dying at the end of the turn only matters if the turn ends. But that's just one of the card's many uses, there's also: using it with Sergeant Sally for a makeshift Shadowflame, use it with the actual Shadowflame, buff a minion to terrifying levels then steal or copy its stats with Void Terror or Faceless Shambler, or simply give it to a humble Imp to kill a 5-cost minion. Power Overwhelming was too flexible for its own good, and was banned from Standard.
  • Ice Lance is a 1 mana Mage spell that freezes a target or, if they were already frozen, deals 4 damage to them. Ice Lance is famous for being a core piece of the Freeze Mage OTK, due to its monstrous power to cost ratio, and notably becomes free when combined with Emperor Thaurissan. Team 5 took multiple steps to hit Freeze Mage throughout the years to reduce its effectiveness, and in the end barred Ice Lance from Standard to make sure it stays down this time.
  • Conceal, a 1 mana Rogue spell that gives all friendly minions Stealth until the start of the turn. Infamously used in conjunction with Gadgetzan Auctioneer, mostly guaranteeing that the merchant stays on the board outside of a Flamestrike or Twisting Nether, allowing the Rogue to cycle through their deck next turn. It's wasn't just Auctioneer though; Conceal could also protect dangerous minions like Edwin VanCleef, Questing Adventurer, or Red Mana Wyrm to prepare to wreck house next turn, and was subsequently shown the door from Standard.

Beta Nerfs

  • Before going any further, there's Beta Freeze Mage, a strong candidate for the best deck of all time. It had excellent card draw, high survivability with Ice Block and Ice Barrier, and a devastating burst combo using Fireball, Frostbolts, and Ice Lances. The whole deck worked like an impeccable machine of efficiency and was nearly unbeatable, especially due to a handful of cards that had to get hit with the nerf bat:
    • Frost Nova, Blizzard, and Cone of Cold were cheap Mage spells that could Freeze either of all of your opponents minions or three of them for a criminally low amount of mana. They were, essentially, "get out of jail free" cards that could be used to buy time to assemble the combo or to protect your life total while dwindling theirs. All three of them have since had their mana costs bumped by one, gutting Cone of Cold and balancing out Frost Nova and Blizzard.
    • Pyroblast used to be an 8 mana Mage spell that dealt a massive 10 damage. It's pretty small potatoes nowadays after its nerf to 10 mana, but at the time, healing was insanely rare, meaning that this would always take off a third of the opponent's health with little ways to get it back. Additionally, while it's weaker than simply double-Fireballing your opponent (2 Fireballs deal 12 damage vs Pyroblast's 10), Pyroblast could be used alongside the 2 mana Frost Nova, meaning that it was less so an expensive, clunky finisher as it was just a gigantic piece of burn, and could be followed up with another Pyroblast+Frost Nova next turn to seal the deal.
    • Alexstrasza, the big, badass win condition of the deck and about the only reason it was viable then and now. She's a 9 mana 8/8 who sets the health of a hero to 15, meaning that at her absolute best, is either "Deal 15 damage" or "Restore 14 health", which was nutty given how little burn and healing there was at the time. She was actually more balanced than she looked, but an oversight made her stupid strong; she also removed Armor, meaning that Druids and Warriors, classes that would otherwise slaughter the deck, couldn't stack up enough health to survive the combo. This ability was removed thankfully, though it had the side-effect of making the Warrior match-up statistically impossible to win.
  • The Priest's Mind Control 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.
  • Blood Imp, a 1/1 for 1 Mana Warlock demon that increased EVERY friendly minions' health by 1, potentially offering HUGE favorable minion trades. If that wasn't bad enough, the Imp has permanent Stealth and was a solid addition to the already widely reviled Zoolock deck - meaning that when the opponent played this card, you just had pray to draw your board clear or got lucky with your random effect to wipe it out soon enough that you still have a board to regain advantage, which is exactly what a Zoolock player wants so they can safely follow up with even more powerful minions; not to mention the fact that it is a Common minion - cheap to create, easy to pick in Arena and could play two of them in a standard Constructive deck. This was fixed by the brutal nerf to the Imp to 0/1 for 1 mana and the ability was changed to "At the end of your turn, give another random friendly minion +1 Health", making it mostly useless.
  • 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 spellnote .

Post-Release Nerfs

  • The vanilla game had a pretty bad problem with card draw engines:
    • Gadgetzan Auctioneer, a 5 mana 4/4 that draws a card whenever the owner casts a spell. It was (and still is, post-nerf) a key piece of Miracle Rogue, a deck based on drawing their deck in one turn with cheap spells to unleash a hellscape of pain on their opponent using Leeroy Jenkins, Questing Adventurer, Edwin VanCleef, or just about anything they could get their hands on. Auctioneer was changed to 6 mana in the Goblins Vs. Gnomes update, which neutered him right up until League of Explorers came along, when the addition of Tomb Pillager brought Miracle Rogue and him back in a much more balanced state.
    • Starving Buzzard was a 2 mana 2/1 Hunter Beast that draws a card whenever a Beast is summoned. When combined with Unleash the Hounds, it was a 4 mana combo that drew 1-6 cards with more than enough mana to spare to brutalize the opponent with the extra combo pieces. Buzzard ended up showing Blizzard that Hunter should never be allowed to have card draw ever lest something like this happen again, and it was ruthlessly changed to a 5 mana 3/2.
  • Speaking of Unleash the Hounds, it was a 2 mana (initially 4) Hunter spell that summoned 1/1 Hounds with charge for every enemy minion. The idea was to give Hunters a different style of board clear than other classes, but in practice it just meant that face really was the place. Indeed, playing too many minions against a Hunter could spell death, as Unleash combo-ed very well with most of Hunter's arsenal to increase the damage even further (Timber Wolf, Leokk from Animal Companion), or draw so many cards that winning would be effortless (Starving Buzzard). It was later nerfed to 3 mana.
  • Leeroy Jenkins used to be 6/2 with Charge 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.
  • Undertaker, from Curse of Naxxramas. It used to be a 1/2 for 1 mana that gained +1/+1 every time a friendly minion with deathrattle was summoned. A simple concept that was heinously broken by a couple of factors; Naxxramas, the expansion that introduced him into the game, brought with it a ton of cheap deathrattle minions like Haunted Creeper and Webspinner, which combined with the similarly cheap Leper Gnome meant that buffing Undertaker in early turns was laughably easy, and could only snowball out of control from there. More importantly was that if Undertaker died early, it didn't matter. Unlike most of the cards here, you didn't have to tailor your deck for Undertaker; all the cards that activated him were good cards in their own right, and as such your deck quality didn't have to suffer simply to accommodate him. There was zero risk and all reward, which also meant that the decks were stupid easy to play. Undertaker's reign of terror lasted for half a year, until a well deserved nerf arrived that made so that he no longer gained health, which was the first nerf to a card outside of the classic set, and the only one at that until the One Night in Karazhan nerfs.
  • When the game first launched, Warsong Commander was 3 mana 2/3 that gave all friendly minions Charge. After an Awesome, but Impractical setup involving Molten Giants and Youthful Brewmasters came to light, Blizzard realized she might become a serious problem later on, so while the then current combo was fairly weak she might rip the game in half later on, and as such she was nerfed to only grant Charge to minions with 3 or less attack. Their original fears unfortunately came true with the release of Blackrock Mountain, which brought the notoriously overpowered Patron Warrior deck into the game. The deck was focused around granting Charge to the Frothing Berserker and the then new Grim Patron to smash the opponent for buckets of damage or clear the board respectively. Almost nothing could stand against it, and as a result Warsong Commander was neutered to a 3 mana 2/3 that gives all friendly minions with Charge +1 attack, completely erasing her original function.

Whispers of the Old Gods Nerfs

  • Leper Gnome was 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 card was eventually nerfed with the introduction of Standard, by changing its attack to 1.
  • On their own, Force of Nature and Savage Roar were pretty reasonable cards. The former was 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 had an absurdly powerful 14 damage, 2 card combo that was run in every single Druid deck. The main problem with the combo was that even though it was no worse than say a double Fireball from a Mage or Cruel Taskmaster+Grommash combo from Warrior, this combo actually scaled with the Druid's board state, as every minion on the board added an additional 2 damage to the combo. Adding to this, the combo was highly flexible, i.e. you could use it in case you needed 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. The Standard update removed this combo from the game, by changing Force of Nature to a 5-mana spell that simply summons 3 2/2 Treants.
  • Ancient of Lore was a 7 mana 5/5 Druid minion that could either draw 2 cards or restore 5 health. Druid card draw spells usually draw quite a few cards, but are pretty expensive, meaning Druids would normally have to give up a turn just to reload their hand. Ancient of Lore solved this issue handily, allowing them to drop a tough minion in the same turn they draw, and it synergized with Mana acceleration spells like Innervate and Wild Growth to regain the lost card advantage used to summon the Ancient. The health gain, while weak compared to the draw option, was still very handy in aggressive match-ups, restoring life and dropping a body in the process. Finally, the exquisite card draw helped Druids search their deck for the aforementioned Force of Nature+Savage Roar combo, and added several points of damage to it should it survive. Ancient of Lore was nerfed to only draw 1 card instead, gutting its utility.
  • Notably averted with Master of Disguise, a 4 mana 4/4 Rogue minion that gave permanent Stealth to a friendly minion. Due to design space reasons and some wacky, out of nowhere gameplay moments caused by randomness (ever give a Mal'Ganis perma-Stealth? It's pretty awesome), her Stealth giving effect was limited to only last until the start of the turn.
  • Molten Giant was a 20 mana 8/8 that had its cost reduced by 1 for every point of health your hero was missing. Created to help give control decks major comeback turns for when they were low on life, it ended up work a little too well in Warlock, who could reliably lower his health with his hero power and get free Molten Giants, letting them either use Sunfury Protector to give the Giants taunt, or Shadowflame to wipe the enemy board. Molten Giant was ultimately nerfed to 25 mana, meaning you have to be very close to death to get freebies.
  • Knife Juggler was a 2 mana 3/2 that dealt 1 damage to a random enemy whenever a friendly minion was summoned. You read that right, summoned, meaning that mass-summoned tokens like from Haunted Creeper, Muster for Battle, and Imp-losion activated this card for several extra points of damage, and with vanilla stats to boot. He was changed to a 2/2, which ended up massively lowering his use rate.
  • Blade Flurry was a 2 mana Rogue spell that destroyed their weapon and dealt its damage to all enemies. Combined with weapon buffing cards like Tinker's Sharpsword Oil, Blade Flurry was one of the most powerful sources of burst damage in the entire game that doubled as an incredible board clearing effect, and there didn't exist a single Rogue deck that wasn't completely based around how busted this card was. It later became a 4 mana spell that dealt its damage to enemy minions instead, a change which made the spell too impractical to use effectively.
  • Big Game Hunter was 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 made 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. This itself was not the problem- it's the fact that it was neutral, meaning that classes with crap for removal options suddenly had access to Shadow Word: Death lite, with a 4/2 attached to boot. BGH alone was responsible for helping Combo Druid and Handlock at the top of the metagame, as they effectively became decks without counters, and gave the already removal heavy Control Warrior another piece of efficient removal. It had gotten so bad that the community would shoot down any high cost legendary minion with 7+ attack, because it died to BGH. To give an idea how broken this card was, even when Big Game Hunter was severely nerfed to 5 mana, he still saw play.

One Night in Karazhan Nerfs

  • Rockbiter Weapon was 1 mana Shaman spell that gave a friendly character +3 attack for that turn. A completely reasonable removal card that was unfortunately given to the same class with Doomhammer, a 2/8 weapon with Windfury. 2 Rockbiter weapons plus a Doomhammer equaled half of your opponents health, and given how much burn damage Shaman has access to, it wasn't difficult to deal with the rest of it. It was nerfed to 2 mana later, making it less effective as a removal spell.
  • Tuskarr Totemic from The Grand Tournament was a 3 mana 3/2 Shaman minion that could summon any random totem. Any of them, including the overstatted Totem Golem, a card draw engine in Mana Tide Totem, and a major damage booster in Flametongue Totem. Tuskarr Totemic could effortlessly snowball games to the point he could decide games the insant he was played. He was nerfed to only summon the basic hero power totems, giving him a much more niche role.
  • Remember the Alexstrasa+Gorehowl combo? The main card in that combo to get nerfed was Charge, which was originally a 1 mana spell that gave Charge to a friendly minion. The sheer power of the combo resulted in the card getting watered down to a 3 mana spell that also gave +2 attack. It was pretty much fine after that, up until the Worgen OTK deck reemerged during the Old Gods era. Combined with Warrior's outstanding card draw and survivability, you had a situation not unlike Patron Warrior where they could kill you in one turn with a massive burst damage combo with little hope of stopping it. Charge got nerfed again, this time to a 1 mana spell where the chosen minion can't attack heroes, most likely killing Combo Warrior forever.
  • Execute was a 1 mana spell that destroyed a damaged enemy minion. Probably the best removal spell ever, as Warrior had access to multiple spells that could ping minions and simply got more as time went on, particularly after Whispers of the Old Gods. The real issue, however, was that because of how cheap it is, faster Warrior decks could run it to deal with big problems without sacrificing much of anything, and simply snowball the game from there. Execute was nerfed to 2 mana; irrelevent for Control archetypes, but painful everywhere else.
  • Call of the Wild from Whispers of the Old Gods was an 8 mana Hunter spell that summoned the three Animal Companions, Huffer, Leokk, and Misha note . The card drops an assload of stats on the board, can draw out board clears on its own without risking your other cards in hand, offers the ability to deal 5 damage to something, and protects and buffs your other minions. Call of the Wild does far too much for one card to be allowed to, and unlike many other cards on this page is not a legendary. Two Calls of the Wild back-to-back is too much for any deck to handle, not even removal heavy classes like Warrior. It was so powerful it had to be nerfed to 9 mana, delaying its effect on the game by 1 turn.
  • Abusive Sergeant, a 1 mana 2/1 that grants a minion +2 attack until the end of the turn. Sergeant is probably one of the best aggro cards ever printed, potentially allowing friendly minions to trade up with minions several points of mana more expensive than them or granting more face damage in case you need to pick up the pace, and has an aggressive statline that allows it to continue getting good trades or peck at your opponents health. Abusive Sergeant was changed to a 1/1 to hopefully curb its influence.
  • Yogg-Saron, Hope's End is a 10 mana 7/5 minion from Whispers of the Old Gods that when played casts a random spell on random targets for each spell you played since the game began. Many players thought it was a joke. They were wrong. Yogg, statistically speaking, will more than likely clear the board and draw his owner plenty of cards, effectively making him a neutral version of the Warlock spell DOOM! and a stronger alternative to Deathwing, but with many, many other potential upsides. Because of the nature of his effect, Yogg can do basically anything, making it impossible to play around him other than holding back your minions so Yogg doesn't kill them, which can just as easily screw you should Yogg-Saron turn out be merciful. In addition to his aforementioned, common functions, Yogg can, as follows: summon an assload of minions for you, buff your board to insane levels, mill your opponent, or in highly hypothetical situations, flat out OTK your opponent. When used as a hail-mary, Yogg can win the game all on his own if a sufficient number of spells are played, and can immediately turn any losing match into a winning one in excessively weird ways no other card can. Yogg is so broken that he singlehandedly dragged Mage into the metagame because of their ability to board clear and survive through spells as well as leading to the emergence of Yogg Druid - an archetype that focus on casting spells to either create tokens or holding many cheap damage spells in their hand to feed Malygos in order to OTK their opponent, that completely overshadowed the intended Beast Druid that the developers have been trying to push for the last few expansions. It eventually reached the point where people played him in official tournaments...and won. This was too much for Blizzard, who gave Yogg a significant nerf where if he is killed, Silenced or bounced back to hand as he's casting spells, the spell spree stops.

Mean Streets of Gadgetzan Nerfs

  • Spirit Claws, from One Night in Karazhan, was originally a 1 mana 1/3 Shaman weapon that gains +2 attack while you control a minion with Spell Damage, and it was indisputably the best weapon ever printed, beating out even Fiery War Axe, a deliberately overpowered weapon. Obtaining the +2 attack is fairly easy for Shaman, as their hero power has a chance to roll a Wrath of Air Totem that has innate spell damage, as well as Bloodmage Thalnos and Azure Drakes to get the damage on demand. Spirit Claws, when swung three times with the buff active, is a 1 mana Pyroblast when aimed at the face and offers psychotic tempo when used on minions, and was so cheap that it might as well cost 0. Spirit Claws had its cost bumped up to 2, meaning that it can no longer be equipped on turn 1 when going first and requiring the coin when going second.
  • Small-Time Buccaneer from Mean Streets of Gadgetzan. He was a 1 mana 1/2 Pirate that gains +2 attack while his owner has a weapon equipped. It almost seemed balanced, right up until you notice that the three classes with cheap, potent weapons (Shaman, Rogue, and Warrior) were also pretty gross aggro classes. With that in mind, Small-Time became a Flame Imp without a downside that also activated Pirate synergies, and could threaten loads of face damage just for the price of 1 mana, especially in conjunction with Patches the Pirate (see the Gadgetzan folder below). Small-Time eventually received a cutting nerf that reduced his health to 1, making him significantly less potent and more easily answered going second.

Journey to Un'Goro Nerfs

  • The worst completed quest to have been on the business end of had to be The Caverns Below, a Rogue quest where you had to play 4 minions of the same name. With minions like the Brewmasters which can put back other minions, and spells like Shadowstep and Gang Up, a crafty/lucky Rogue could complete this quest before their fifth turn! And the reward for completion? Crystal Core, a 5 mana spell which sets all of your remaining minions' stats (deck, hand, and on the board) to 5/5! What makes it particularly nasty is that 1-mana Charge minions such as Southsea Deckhand, Patches, and freaking Stonetusk Boar keep the stat boosts, which can set up OTK combos with the remaining bounce effects. Worse, Crystal Core can be played for a measly 2 mana thanks to Preparation! This deck archetype is so powerful and popular that it forced every single deck to tech in counters to it in order to be viable. A deserved nerf bumped up the quest requirement from 4 to 5, making it harder to blow out your opponents.

Knights of the Frozen Throne Nerfs

  • Fiery War Axe, originally a 2 mana 3/2 Warrior weapon, was often considered one of the most powerful Warrior cards ever printed due to its sheer power and cheap cost that would allow the Warrior to kill off almost every 2 drop the opponent played while still retaining a 3/1 weapon ready to swing again. No viable Warrior decks ever went without this weapon and the win rate of a Warrior increased by at least 50% if the player draws this card in their opening hand. War Axe eventually got the axe and was changed to a 3 mana weapon instead, turning it from one of the strongest weapons in the game into one of the worst.
  • Hex was a 3 mana Shaman spell that transforms a minion into a 0/1 Frog with Taunt. There's no reason to make this more complicated than it is; this was the best removal option in the entire game by a country mile, and most Shaman match-ups involved the Shaman's opponent playing around it as best they could while trying to take them out. Hex was changed to 4 mana, making it in line with the Mage's Polymorph, which possesses a similar effect.
  • Innervate, a 0 mana Druid spell that formerly gave the owner 2 mana crystals for that turn only. This card could do some insane stuff very early, such as: a turn 8 Ultimate Infestation, a turn 7 Ysera, 5 mana worth of tokens ready to be buffed, and an extra set of mana to use for combos when already at ten mana (such as Malygos shenanigans). Even in the vanilla game, a turn 1 Chillwind Yeti was enough to make anybody concede on the spot. Innervate was singlehandedly responsible for making sure Druid stayed in the meta-game, dodging nerf after nerf, until Knights of the Frozen Throne finally knocked it down to size by reducing the amount of mana it gave to 1, making it on par with the Rogue card Counterfeit Coin.
  • Murloc Warleader, 3 mana 3/3 Murloc that originally gave friendly Murlocs +2/+1. Warleader functions as the key enabler of Murloc decks, due to granting massive stat bonuses for little mana, but because Murlocs kind of, well, sucked, he never thrived up until League of Explorers and Journey to Un'Goro. League introduced Anyfin Can Happen, a spell that allowed Murlocs to be usable as an OTK package, while Un'Goro brought forth Gentle Megasaur, Rockpool Hunter, and Sunkeeper Tarim (see Un'Gorobelow for his entry), a set a minions that allowed Murlocs to stay on the board, ready for those juicy buffs. Warleader's influence was enough that Knights of the Frozen Throne removed the health bonus from his effect, making large Murloc boards much less sturdy.
  • Spreading Plague, from Knights of the Frozen Throne, was a 5 mana Druid spell that summons a 1/5 minion with Taunt, and summons more of them until you possess as many minions as your opponent. It's comparable to Frost Nova in that it stalls the game until you can get your bigger, better plays, which is a big deal for a class with poor early-game. Additionally, the 1/5 tokens can be buffed by Mark of the Lotus and similar cards to build a massive board from just a few resources, while protecting higher priority targets like Fandral Staghelm and Vicious Fledgling. Even without any synergy cards, Spreading Plague on its own stops aggro in its tracks, and if they have 7 minions on the board, it may as well be a death sentence. Spreading Plague was announced to receive a nerf to 6 mana roughly 3 weeks after Knights was launched, making it the fastest recorded nerf in the entire game.

    Vanilla Game 
  • Two Divine Spirits note  used on a decently sized minion will give that minion a very high health pool, and casting Inner Fire on it note  gives the opponent a problem that hits as hard as it can take. Husky Starcraft and his friend Sinvicta discovered that, if you use Lorewalker Cho note  and can get your opponent to co-operate with you, you can very easily get a Minion up above 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. However, this strategy came back in Journey to Un'Goro with a vengeance with the addition of more Silence, cheap high health minions and especially cards like Radiant Elemental and Shadow Visions.
  • Flamestrike, a 7 mana spell that deals 4 damage to all enemy minions. It's one of the Basic cards, so everyone has one. Yet it is the single most feared Board Clear in a Mage's arsenal, and it is not an exaggeration to say that an 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.
  • 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.
  • Tirion Fordring is an 8 mana 6/6 Paladin minion with Divine Shield and Taunt, itself already a solid deal, and equips his owner with a 5/3 Ashbringer when he dies. Tirion's base body alone is worth paying the mana cost for, capable of trading 2 for one with mid-sized creatures, but the Deathrattle is where he truly shines. A 5/3 weapon can deal half of the enemy hero's life on its own or destroy up to 3 more moderately-costed minions, giving its user time to develop their own board and seal the game. Tirion is widely considered the king of lategame matchups and is fully capable of ending games by himself. That said, all of this was completely intentional. Paladin, as a class, was meticulously crafted with this one showstopper in mind, and as a result has a hard time winning games without him. It's only when Paladin had access to other stupid powerful cards (Muster for Battle, Mysterious Challenger) that made up for Paladin's other weaknesses that Tirion became a problem, because he went from a reward for reaching the endgame to another broken card that could make the enemy cry.

    Curse of Naxxramas 
  • Mad Scientist. It's a 2/2 for 2 mana, itself a merely slightly below average statline, with the obscene deathrattle of putting a random secret from your deck into the battlefield. If it merely drew a secret, it would be crazy, as it lets you tutor for important cards like Explosive Trap and Ice Block. Instead, it puts the damn thing into the field at no extra charge. Hunter secrets cost 2 while Mage secrets cost 3, meaning that this card is worth 5-6 mana (1.5 for the body, 1.5 for the specific draw, 2-3 for the secret) in value for something that can be absentmindedly dropped on turn two, ready to contest any 1-drops or 3/2s your opponents play. Out of all the cards booted from Standard once formats came around, even with several fan favorites leaving, there was universal rejoicing that Mad Scientist was finally gone.
  • 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.
  • Zombie Chow is a 1 mana 2/3 with the Deathrattle of restoring 5 Health to the opponent's Hero. This card's incredible stat line and the lack of good 1-mana non-aggressive minions means that almost every single deck archetype except for Face Hunter will run this card because it will trade off a 2 mana minion and has a big change to survive. This card singlehandedly slowed down the meta to let control decks like Priest gain a leg against aggressive decks but its brokeness had to be felt in Arena because it was considered an auto-pick every time it showed up on screen.
  • Sludge Belcher, a 5 mana 3/5 Taunt minion with the Deathrattle of summoning a 1/2 Slime that also has Taunt. This card's annoying Deathrattle means that it has to be killed twice in order to completely being get rid of it and its solid body is excellent for control decks to bait out Silence. Like Zombie Chow, it was also considered an auto-pick when offered in Arena.

    Goblins vs. Gnomes 
  • The notorious Dr. Boom. He's a 7/7 for 7 mana that summons 2 1/1 Boom Bots into battle with him, with each of them dealing 1-4 damage to a random enemy on death. 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. Adding to this, he costs 7 mana, which means he can be played after a particularly high value 6 drop, a list which includes but is not limited to the aforementioned Savannah Highmane, and the later mentioned Emperor Thaurissan and Mysterious Challenger, meaning that when he shows up the opponent likely lacks the required removal to beat him. Finally, there's his flexibility; Dr. Boom will provide nothing else of use other than astronomical value, which despite what it sounds like is incredibly good. This means that while he's not the best card in the game by any means, his sheer power and ease of use mean that there are few decks that wouldn't be improved with Dr. Boom, even a select few aggro or combo decks.
  • Mechs were a brand new tribe introduced with this set in the hopes of giving newer players a deck that was easy to put together, as most of its best cards were commons and had very obvious synergy with each other, so all you had to do was type "Mech" in the in-game search engine and there's the deck. Unfortunately, Team 5 went a little too all-in on the idea, causing Mechs to be far stronger than they had any right to be. Mechs, mostly, were aggro cards, but instead of being frail damage dealers, they were based on flooding the board and then using their synergy cards to beat down the opponent with no hope of fighting back. Particular offenders include:
    • Mechwarper, the centerpiece card of all Mech decks, is a 2/3 for 2 mana that reduces the cost of all Mechs in hand by 1 mana. Most Mechs are very efficient for the cost to start with, like the 3/4 for 3 Spider Tank and the 1/2 Taunt Divine Shield for 2 Annoy-o-Tron, and are also quite cheap, meaning that if Mechwarper survives turn 2, it's very likely the opponent will spam the board with multiple minions for nothing at all, and even to this day there is no AoE spell that would be capable of dealing with such a board outside of Doomsayer. Plus, this effect stacks; two Mechwarpers is an absolute nightmare that can create unwinnable circumstances, especially when combined with...
    • 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. Plus, it has a chance to spawn overstatted minions like Millhouse Manastorm. The only downside to using it is the possibility it might spawn Darnassus Aspirant or Doomsayer (which isn't that bad if you're losing board control), but considering how often it hits compared to how often it misses, who cares?
    • Goblin Blastmage, a 5/4 for 4 mana Mage minion that deals 4 damage split amongst all enemies if you control a Mech. This card, combined with Mechwarper's minion spam, made it nigh-impossible for an opponent to catch up if they were behind, because Blastmage would kill any threats they put down or did enough face damage to just go for the kill. The vanilla stats, while lax nowadays, were a big deal back then because he could kill most minions and likely survive, while being sturdy enough that it survived basic removal like Frostbolt.
  • 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. On top of it's status as a cheap spell at a time when cheap spells were invaluable for Mage, it's effect is randomness gone horribly wrong; as many pro players 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. 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.
  • Velen's Chosen, a 3 mana Priest spell that buffs the minion by 2/4 and gives it +1 Spell Damage. This card is considered one of the best Priest cards ever printed in the game because its cost allows the Priest to buff their early game minions to be a giant trading machine that the Priest can keep healing back. That is without talking about the Spell Damage it offered, which allows the Priest to buff their board clear to be more mana-efficient. Many players bemoan the loss of this card when Standard hit and it was still used as a measuring stick when creating Priest cards, especially spells or buffs. This card is so powerful that the community mocked Blizzard when they tried to print its Poor Man's Substitute Power Word: Tentacles, a 5 mana spell that buffs for 2/6.
  • Muster for Battle is a 3 mana spell that allows the Paladin to summon 3 1/1 Silver Hand Recruits and equip a Light's Justice. This card's effect effectively allows the Paladin to summon 3 minions in one turn for 3 mana, which is quite good on its own when combined with Blessing of Kings for 4 mana, but the thing that made this card completely broken is that it also equips the Paladin with a 1/4 weapon, effectively allowing them to profit even if the opposing Hero uses a board clear.

    Blackrock Mountain 
  • Emperor Thaurissan. He's a 5/5 for 6 with the 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.

    The Grand Tournament 
  • Mysterious Challenger, a 6/6 for 6 mana Paladin minion that puts up to 5 secrets from your deck into the battlefield for free. 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. On top of this, 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.

    League of Explorers 
  • Tunnel Trogg, a 1/3 for 1 mana that, whenever you play a minion with Overload, gains +1 attack per crystal overloaded. Trogg's statline makes it hard to kill early on without a good earlygame removal card like Fiery War Axe, and despite what it looks like its effect can quickly get out of control, the main reason for which is because of its companion cards Totem Golem and Feral Spirit. The former is an overstatted 2-drop with 1 Overload to compensate, which this card turns into an advantage, while the latter summons 2 2/3 Spirit Wolves with taunt that can protect the Trogg, while giving it +2 attack due to the Overload. The final straw to "broken" territory was Flamewreathed Faceless added in Whispers of the Old Gods, a gigantic minion for a piddly 4 mana that demands a completely different answer from Trogg - meaning that if you chose to mulligan so you can kill Trogg, you get smacked down by Flamewreathed, and vice versa.
  • 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.
  • Naga Sea Witch, a 5 mana 5/5 with the effect of turning every cards in your hand to cost 5 mana, became this in Wild after a buff allowed her effect to apply before any discount effect. This means that the Giants, which are so expensive one needs to build a deck around them to use, can now cost 0 with Naga Sea Witch on the board with only very minimal condition requirement, allowing for a field full of 8/8s as early as turn 5.

    Whispers of the Old Gods 
  • Flamewreathed Faceless, a 4 mana 7/7 Shaman minion with 2 mana Overload, quickly became this within weeks of the expansion. The sheer tempo created by this minion along with the nerf of Big Game Hunter to 5 mana means that the Shaman player can reliably hit the opponents face while forcing them to trade into it, or waste spell cards, if they don't want to outright lose the game without the Shaman player sacrificing anything. What's worse is that the new Standard pushes out many Neutral Taunt minions and healing while Aggro Shaman only lost Crackle, which 2 copies of this card have done more than enough to replace it. The rotation of Tunnel Trogg and Totem Golem eventually scales down the power scale of Aggro Shaman and made this card much worse.
  • Thing From Below is a 6 mana 5/5 Shaman minion with Taunt that reduces its own cost by 1 whenever its player summons a totem throughout the game. Which is often. It is very difficult to play this card for the default cost of six due to how many powerful, low-cost totem cards there are like Totem Golem and Mana Tide Totem, making it more like a 4 mana card at most and a 0 mana card most of the time. This is without getting into the common strategy with it: Shamans are very good at making frail but massive boards with just a few cards, making it easy to bait out board clears then immediately follow it up with two Things, forcing the opponent to have yet another answer. Combined with Thunder Bluff Valiant and the aforementioned Flamewreathed Faceless, it's very easy for a Shaman to keep pumping out threats until the opponent just doesn't have answers anymore.
  • Fandral Staghelm is a 4 mana 3/5 Druid minion who combines the effects of your Choose One cards. When played early on, Fandral can combo with cheap Choose One cards like Wrath, Living Roots, and Raven Idol to give massive card advantage and board presence, and unlike many cards of his cost is still relevant in the endgame, capable of working with Nourish and Ancient of War. Druid's mana acceleration abilities (like Innervate, Wild Growth etc.) make him even stronger, because they do the crazy crap sooner than most decks will be able to handle, and with proper execution and luck, can allow his owner to play 7 cards at once as early as turn 3. The 2017 rotation massively reduced his power, but he's still quite handy.

    One Night in Karazhan 
  • Maelstrom Portal is a 2 mana Shaman spell that deals 1 damage to all enemy minions while summoning a 1-cost minion for yourself. In theory, this card is pretty much fine; it's a buffed Arcane Explosion, that nobody played, so what's the big deal? Well, they gave it to the one class that would commit murder to get their hands on Arcane Explosion as it is, and then they tacked a bonus effect on top of it. Shaman's worst match-up, historically, has been Zoo Warlock, a deck based on summoning a bunch of cheap minions with potent effects, stickyness, or above-curve stats. Shamans normally lacked the Area of Effect damage required to deal with the deck outside of the costly Lightning Storm and Elemental Destruction, but Maelstrom Portal is not only cheap, it summons another minion prepared to kill whatever the Zoo player plays next. Add in the on-demand spell damage through the hero power to turn it into a 2-mana Consecration and it's utility in match-ups other than Zoo, and Maelstrom Portal ended up being an auto-include from day 1.

    Mean Streets of Gadgetzan 
  • Patches the Pirate. He's a humble 1 mana 1/1 Pirate with Charge by nature, but in the event that you play any pirate, he blasts himself out of your deck into the battlefield ready to fight. What should be a simple effect to give Pirate decks a small boost ended up being the combined form of multiple cards on this page. He's a reverse Mad Scientist, in that he gives all of your pirates a one-time Battlecry of "Draw and summon a Stonetusk Boar". When used with N'Zoth's First Mate, you essentially get a cheaper Muster for Battle, an already undercosted card, with one less 1/1. Even just getting him off of Swashburglar or Southsea Deckhand is already better than Alleycat. While a meager 1/1 doesn't seem like much, it's a 1/1 that you got for free, meaning free face damage, a free ping, a free activator for Bloodsail Cultist, or a free target for buffs like Cold Blood. Even classes that physically cannot use pirate synergies run Bloodsail Corsair just for Patches' effect. He is that good.
    • Patches becomes even more broken in Tavern Brawl game modes where you can field multiple of him in a single deck. Such is the case in All Star, where a player may have 22 copies of him in the deck, resulting in a constant stream of 7 damage to the face from the very first turn.
  • The Drakonid Operative can be quite the game-ender. It's a 5 mana 5/6 Priest Dragon that, if you're holding a dragon, Discovers a card in the opponent's deck. In addition to giving you a free card, an edge in the fatigue game, and information about what your opponent isn't currently holding, this can allow you to pick up very powerful cards because, unlike other Discover cards, this one is guaranteed to only pull good cards. Cards like, as follows: your opponent's Drakonid Operative, which can create an endless train of Operatives, big-time legendaries like Ragnaros or Reno Jackson, burn spells that Priest usually isn't allowed to have like Fireball, nasty survival tools like Ice Block and major lategame winners like Anyfin Can Happen, which can turn your opponents' stratagems against them. It's especially nasty when combined with Brann Bronzebeard, letting take another look at their deck for information and taking whatever you please. Drakonid Operative is so powerful that he, Netherspite Historian and the newly introduced Primordial Drake essentially carried Dragon Priest into the meta of the Year of the Mammoth despite rotation causing Dragon Priest to lose a lot of vital cards.
  • Kazakus, a 4 mana 3/3 Kabal note  minion. If the player has no duplicates in their deck at the time of his summoning, Kazakus allows his owner to build a custom spell that can cost 1, 5, or 10 mana with 2 effects of correlating power. The sheer amount of abilities the potion can have is astronomical, which makes it complicated to explain, but the basic gist is that Kazakus' potion can be a board clear+heal, a damage spell with a fat demon attached, a N'Zoth that draws cards, or basically anything else, all of which are undercosted. The flexibility is utterly insane, with the only tradeoff being the somewhat RNG nature of the choices. It gets outright nightmarish when combined with Brann Bronzebeard, allowing the player to get another freaking spell, almost guaranteeing victory because not even the RNG aspect can balance it out; by getting 2 Kazakus spells, the odds of obtaining potions you actually want goes up.
  • Jade Idol. It's a 1 mana Druid spell that either summons a Jade Golem or shuffles 3 more Idols into the deck. The deck that uses it, Jade Druid, isn't particularly good, but it had a nightmarish side-effect on both the Gadgetzan and Un'Goro metagames - it removed anti-aggro control decks from the game singlehandedly. This caused the meta to twist and churl until only decks that were faster than Jade remained - even the control decks needed to be proactive in the lategame instead of just turtling, meaning their aggro match-ups became weaker. This eventually got so frustrating that Blizzard themselves got fed up with it and printed the Skulking Geist in Knights of the Frozen Throne, a 4/6 for 6 mana that destroys all 1-mana spells in both hands and decks. All of them. And even its presence was not enough to dissuade Jade Druid from the ladder after that expansion's launch.

    Journey to Un'goro 
  • Primordial Glyph is a 2 mana Mage spell that Discovers a spell and reduces its cost by 2. The fact that it Discovers the spell is a huge deal, because you can just go digging for burn damage, removal, or defenses on a whim, and the sheer quality of Mage spells as a whole means that it's difficult to be mad with whatever you get. Additionally, the cost reduction negates the main weakness of expensive Mage spells, because now you can actually play more cards in the same turn you nuke the opponents board with a Flamestrike or a Meteor. It gets disgusting in the event you pull a card that's already efficient like Fireball, which can set up some nasty burst combos. In rare cases, and if the other two spells were not to your liking, you could discover another Primordial Glyph which gets reduced to free for another shot at getting what you want, or to proc another effect that requires a spell being cast, like that of Mana Wyrm or Open the Waygate.
  • Sunkeeper Tarim, a 6 mana 3/7 Paladin Legendary minion with Taunt and the effect of turning every other minion on the field to a 3/3. This card is absolutely bonkers on its own with the Paladin's playstyle of summoning tokens and controlling the board, since it allows even the humble Silver Hand Recruits to now trade evenly with formerly giant minions. What pushes it into broken status is its absolutely insane synergy with the Murloc package. Murloc Warleader's buff is continuous so it will not be overwritten by Tarim's stat-altering ability, turning a swarm of mere 1/1 Murloc tokens into a wave of fearsome 5/4 beaters. The fact that he has Taunt lets your Murlocs survive another turn, enough for you to drop a Gentle Megasaur to adapt the Murlocs and crush the opponent. It's no wonder that he saw play in almost every viable Paladin deck along with Tirion (see above).

    Knights of the Frozen Throne 
  • The most reviled card in the expansion easily goes to Ultimate Infestation, a 10-mana Druid spell that deals 5 damage, summons a 5/5, gives the Druid 5 armor, and draws 5 cards. The main weakness of the grindy Jade Druid was that it, too, eventually runs out of steam without something like Gadgetzan Auctioneer to combo with Jade Idols, but Ultimate Infestation generally remedies that, on top of creating a board swing and giving extra armor to extend the Druid's stamina.
    • The insanity just got worse with the Standard Blood Magic brawl, where you can cast spells with health as opposed to mana. Ultimate Infestation on turn 1 was not a pretty sight, especially when the armor it bestows allows the Druid to throw out a few more spells without endangering his health.
  • Shadowreaper Anduin, an 8 mana Priest Hero card that kill all minions with 5 attack or more and change the Hero Power to Voidform - a Hero Power that deal 2 damage and then refresh itself whenever the Priest player play a card. Sound fair in paper, but the Hero Power has insane synergy with Raza the Chained, a 5 mana Legendary minion which allows the Hero Power to cost 0 for the rest of the game if your deck has no duplicate, suddenly allows the Priest to pump out 6-8 control damage every single turn for 0 mana. The fact that this card fills in two holes of Priest in one fell swoop, namely the ability to end the game through the insane amount of damage every single turn with Raza and deal with many big minions since Lightbomb rotated out, led him to cause chaos in both Standard and Wild and Priest - a class has traditionally struggled, suddenly pushed to prominence through this synergy alone. If Spreading Plague and Ultimate Infestation took the silver and gold medal for most powerful cards this expansion, Shadowreaper Anduin took the bronze for his synergy with Raza.

    Arena 
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.
  • 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 less effective 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.
  • Murloc Knight was once 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. Most importantly, it's common, meaning it's very hard not to get one during a draft. It got so bad Blizzard directly introduced two lowly statted murlocs in League of Explorers just to nerf it, and has steadily received more nerfs over time, making it much less powerful.
  • Murloc Knight's torch was passed on to Keeper of Uldaman, a 4 mana 3/4 Paladin minion that changes the stats of a minion to 3/3. Remember how Paladin didn't have hard removal? Well then this'll be weird, because now they can handle any big minions thrown their way, when previously they were restricted to just lowering its attack without actually clearing it. Not only can Keeper kill the affected minion without dying, she can also buff her allies as well, granting even a lowly Silver Hand Recruit +2/+2.
  • What shot and keep Rogue into top tier in Arena and competing with Mage isn't just their mana-efficient basic and classic cards (Backstab, Eviscerate, Tomb Pillager etc.) but it is the class's Hero Power. Dagger Mastery allows the Rogue to equip a 1/2 weapon, which in Arena play is essentially 2 of the Mage's Hero Power (Fireblast) that you can control and hold back to kill or weaken a minion in a game that focus on keeping a minion alive to have more favorable trade. This Hero Power is so broken that many Rogue Arena decks tend to draft less 2 mana minions than other classes because their turn 2 play are usually Dagger Mastery to kill a 1-drop and save their card slots for better cards.
    • Envenom Weapon is one of Rogue's strongest cards in Arena — giving their weapon Poisonous turns their already good Hero Power into 2 charges of hard removal, perfect for taking out even the toughest Taunt minions to either push damage or trade better using their other minions.
  • Abyssal Enforcer, a 7 mana 6/6 Common Warlock Demon that deals 3 damage to all other characters. It's a Flamestrike with a huge body attached, and while it damages its allies as wellnote , that doesn't matter that much when everything that can fight with it is dead, allowing the Enforcer to slaughter anything that drops next or mash face until the opponent answers it. It cannot be understated how outrageously powerful this card is; Warlock, previously one of Arena's joke classes, instantly upgraded to the number one slot just because of this powerhouse, and getting enough of them generally guarantees the 12 wins reward.
  • Vicious Fledgling earned the nickname of "Dr. 3", taking after Mysterious Challenger and Dr. Boom. This 3/3 for 3 mana adapts each time it hits the enemy hero — and if it gets Windfury it gets another swing for another adaptation, quickly spiraling out of control as it accumulates more and more buffs. Due to Arena's lack of efficient removal, if you can't get a Taunt in the way so that you can clean up the Fledgling through combat damage, the Fledgling can singlehandedly cause an Arena loss. The more infuriating part is that this is a neutral minion so no matter what class you're up against there's always a chance the opponent has it. A patch has reduced the chance of Fledgling appearing in a draft, so while it's still a great headache if it shows up, it's become a much rarer headache.
  • Spikeridged Steed is a 6-mana Paladin spell that gives a minion +2/+6 and Taunt, while also causing them to leave behind a 2/6 with Taunt if they die. Essentially, turning any minion of your choice into a stronger version of the infamously sticky Sludge Belcher. Using it even on a simple 1/1 creates a wall capable of soaking at least 13 damage; using it on anything larger lets them survive through troublesome trades.
  • Mage has been one of the best classes to take into Arena due to the amount of card generating effects available to the class. Add to the fact that these cards were random or Discovered and nobody could play around what had been generated. Between Cabalist's Tome, Babbling Book, Primordial Glyph, and Shimmering Tempest, a Mage could conveniently get the spell they need to stage a turnaround or secure their victory. In fact, a few Mage cards on their own are Arena Game Breakers, which adds to the frustration when one discovers them:
    • 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.
    • Firelands Portal, a 7 mana common Mage spell that summons a random 5-cost minion and deals 5 damage. Flamestrike is literally the only thing you wouldn't pick this over, and even then its a close contest. Firelands Portal's insane tempo swing from taking a minion and then playing one of your own can win a match in one fell swoop, and since it's a common you can just do it again and again until you win. Sometimes the 5-cost minion will be junk like Faceless Manipulator, but other times it'll be something revolting like Earth Elemental.
  • The Death Knight cards of the Knights of the Frozen Throne expansion open up drastically new playstyles in constructed. In Arena, though, they are absolutely game-changing and can be the sole cause of a player turning the game around. Their Legendary rarity reduces the rate at which a player might be able to encounter them, but there's nothing stopping them from Discovering a Death Knight card. The ability for the Death Knights to win games alone resulted in them being removed from the Arena draft pool.

    Other 
  • There are quite a few strategies to cheese the Heroic adventure bosses, but the most common one is the aforementioned Divine Spirit-Inner Fire combo. Unlike most constructed decks, bosses will rarely have hard removal, meaning that the buffed creature can stick around and do heavy damage. Adding to this, the player doesn't even have to bother trading with enemy minions, as the AI will just keep throwing their minions at your gigantic monster until they have nothing left. This only time this does not work is against the Steel Sentinel, who reduces all damage it takes to 1.
    • Another common strategy is somehow giving them Majordomo Executus, usually by exploiting boss deck choices like Mindgames. When Majordomo dies, he replaces his owner with an 8 HP Ragnaros that also changes their hero power to dealing 8 damage to a random enemy. While the hero power can be strong, it's ultimately going to be far weaker than whatever the boss had before, and Ragnaros' pitiful health means that he'll invariably die before it becomes an issue.
    • Kel'Thuzad continues to be quite helpful in the side modes. If you manage to get a Taunt minion to stick onto the field and then drop Kel'Thuzad behind it, the AI will flat out stop attacking no matter what until it can somehow remove Kelly without killing the Taunt. This lockout strategy can easily cheese any boss without a good means to destroy him, and if you happen to be playing Priest (who can heal him) or Shaman (who can duplicate him), it's basically bullying.
    • The Animated Armor boss has the special ability that it can only take one point of damage at a time. No matter how high his stats get, C'thun's effect does damage one point at a time. If it could, the AI would probably cry when C'thun is played.
  • The undisputed king of the Wild format is N'Zoth, the Corrupter, a 10 mana 5/7 introduced in Whispers of the Old Gods who summons every Deathrattle minion that died that game. While already good in Standard, capable of summoning Sylvanas Windrunner, Tirion Fordring and Cairne Bloodhoof, it gets crazy when you simply take a look at how much Deathrattle crap there is in Naxxramas and GvG. You've got, as follows: the bulky Taunt minions Sludge Belcher and Deathlord, the annoying critter spawners like Haunted Creeper and Nerubian Egg, and the infamously sticky Piloted Shredder as well as its much bigger cousins Piloted Sky Golem and Sneed's Old Shredder. A Wild N'Zoth board is nigh-impossible to deal with, to the point where even Deathwing can't save you, and managing to get yourself out of such a situation either means you played N'Zoth yourself or you deserve a goddamn trophy.
  • Certain unlikely card combinations can utterly break the game. Observe, what happens when you combine Mal'Ganis with Stealth, and the enemy does not have sufficient area of effect spells.note  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 
  • While Tavern Brawls encourage all kind of unique strategies, most at least have some sort of major flaw to them. That cannot be said for Yellow-Brick Brawl, where Dreadsteed cranks this Up to Eleven. He's a 4 mana 1/1 with a deathrattle that summons a new Dreadsteed on death, not so bad in standard play, since each replacement Dreadsteed will lack any buffs the previous one had. In this Tavern Brawl however, Dreadsteed is almost impossible to beat. Dorothee's effects are thus that minions to the left of her have Charge and the minions to the right of her have Taunt. This means that each and every Dreadsteed summoned will immediately be able to charge in and summon another one until your opponent's entire board is cleared. It's just as bad if Dreadsteed is put on the right, as everytime the opponent kills one, another Dreadsteed with Taunt will immediately come back, making it impossible to deal any damage to the enemy hero without the use of spells or hero powers. Unless you bring alternative means to remove minions (Transforming, Shuffling, etc.) Dreadsteed is impossible to shut down.
    • Unless you have Mekgineer Thermaplugg, a 9 mana 9/7 that summons a Leper Gnome note  whenever an enemy minion dies. Basically, just place the ol' Mekgineer to the left of Dorothee and kill one of the Dreadsteeds, and watch the magic happen. note 
  • Part of the parcel of being a digital card game, the game has some nasty glitches and interactions:
    • Nozdormu's brain-breaking glitchyness came in full force with the addition of Joust during The Grand Tournament. 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 too 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.
    • On launch of League of Explorers, there was a dangerous bug with Unearthed Raptor that ended up getting its abusers a lot of free wins. Raptor, by default, is a 3 mana 3/4 that copies a friendly Deathrattle effect. When combined with Brann Bronzebeard, who triggers your Battlecry effects a second time, this can stack up for even more Deathrattles. The bug kicks in once you started using a second Raptor to dupe the effects of the first Raptor; for some reason, if you duped the Deathrattle effect enough times, the game will force a crash for the opponent (sometimes both players), giving the Rogue player a free win. It was quickly hotfixed, but it was scary time for players everywhere. You know, except the Rogues.
    • The aforementioned Fandral Staghelm (See Whispers of the Old Gods above) was also the cause of a bizarre, powerful Wild-only glitch with Dark Wispers. Dark Wispers is normally a 6 mana spell that either summons 5 1/1 Wisps or gives a minion +5/+5 and Taunt. Fandral causes it to do both, but for some reason he also removed the minion restriction, meaning the player could give himself +5/+5 and Taunt. While the Taunt and +5 health are obviously good, the extra attack was utterly ballistic, because it lasted forever. Your hero can swing for 5 damage every turn with no restrictions and maintain it during the opponents turn, meaning that any minions that attacked would take 5 damage and likely die. It was swiftly patched, for good reason. If nothing else, it was kinda cool while it lasted.
    • The Shadow Visions + Radiant Elemental loop, as discovered by Disguised Toast, is a three card combo introduced in Journey to Un'Goro consisting of two Radiant Elementals and a copy of Shadow Visions, with the other copy in the deck. Because of how animation times work in Hearthstone, a crafty player can simply play the Elementals to reduce the cost of Shadow Visions to 0, then use Visions to discover the other copy of it, then play it again and again and again. From your perspective, you're just playing the same card over and over, but from your opponent's perspective, they have to sit through a short animation of the card being played every single time. Spamming Shadow Visions enough forces your opponent to watch the animations on their turn, skipping their turn entirely. This was swiftly hotfixed, thankfully.
    • In the Spellbook Duel Tavern Brawl, players have a deck of 10 unique cards, and instead of drawing from the deck, they discover a copy of a card in their deck.note  Gnomeferatu has a Battlecry of removing the top card of the opponent's deck, which actually reduces their discover options as you play more of her. Once a player is reduced to 3 or fewer cards in their deck, a bug occurs that prevents that player from taking any action.
      • This can be countered with another Game-Breaker, Jade Idol, which in this game mode might as well read "After a bit of setup, you may turn every card you draw into a big/big Jade Golem for 1 mana each".note 
      • Predating Gnomeferatu in this regard is Deathlord + Loatheb combo. Deathlord's deathrattle ability drags a minion out of an opponent's deck into the field. In normal games this ability can backfire spectacularly, but in Spellbook Brawl, this has the effect of preventing the enemy from discovering that minion for the rest of the game. While it does take some setup due to Deathlord being more expensive than Gnomeferatu, once you drag out all your opponent's minions from the deck, they can only discover spells, at which point Loatheb's battlecry ability ensures your opponent at best can only play one weak spell per turn due to having their spell cost bumped up by 5, possibly every turn.
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