These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Designated Hero: The subtitle is Heroes of Warcraft. That said, two of the "heroes" are Gul'dan (an evil warlock from the franchise's backstory) and Garrosh Hellscream (the Big Bad of Mists of Pandaria).
It's possible that "heroes" is used in the sense of "controllable powerful faction leader" as it is in Warcraft (and for that matter the Defense of the Ancients: All-Stars mod)
Lord Jaraxxus. Originally a raid boss from World of Warcraft, Jaraxxus appears in Hearthstone as the Warlock's unique legendary card, and he quickly became probably the most popular character in the game thanks to a combination of his glorious voice acting, his hilarious emotes and quotes, and for being a total standout amongst the cards of the game: if Jaraxxus is successfully summoned, he outright replaces Gul'dan as the hero with an 3/8 weapon and a game changing hero power, meaning that Jaraxxus isn't just awesome, he's a card to be feared as well. Upon summoning, he drops his famous quote, "YOU FACE JARAXXUS, EREDAR LORD OF THE BURNING LEGION! " Finally, it seems to have become recognized, as in one set of patch notes Blizzard specifically references him.
Battle.Net Patch Notes: Winning a game as Lord Jaraxxus will now properly grant credit towards unlocking the Warlock golden hero. You win... BUT YOUR WORLD IS STILL DOOMED!
Annoy-o-tron, a 1/2 Mech with Divine Shield for 2 mana, is one of the most popular cards in the fandom for its hilarious yet adorable emotes and surprising effectiveness in Mech decks.
Two Divine Spirits note A spell that doubles a minion's Health 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 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 which puts a copy of any spell used into the other player's hand and can get your opponent to co-operate with you, you can very easily get a Minion up above 1 billion health.
Explosive Overclocking: Raising the minion's health too high in this combo (specifically, past 2,147,483,647) will cause it to instantly die as its health overflows and becomes a negative number.
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 spell has a similar, if less immediate effect: 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 was 8 mana in 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 deserves a special mention. 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 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 assuem they have by Turn 7) but without using your really good cards.
The Priest's Lightspawn minion has as much attack as it does health. This means if the Priest decides to use any health-increasing spells, you'll be dealing with something that not only hits like a truck, but can take a beating. Easily neutered by a Silence, but Silence can be either non-optimal to add to your deck or simply refuse to be drawn when you need it.
Lord Jaraxxus is combines this with Death or Glory Attack. On one side, summoning him puts you at 15 hp cap, and more often than not makes you unable to do anything else for the turn, allowing your enemy to respond in kind. On the other hand, his hero powernote Summons a 6/6 for 2 mana can be considered one of, if not the most powerful in the game, and can quickly overwhelm your opponent with sheer brute force if they fail to respond immediately.
It's Easy, so It Sucks: Veteran TCG players are quick to slam Hearthstone for being overly simple, due to the lack of playing out of turn, due to a small card pool, etc etc.
Junk Rare: Several Epic cards are of limited use beyond 100 crafting dust (the value of a more useful Rare card). Kidnapper is arguably the worst of the bunch, but as a class, Warlock got shafted since all three of his Epics are underwhelming for their cost.
Most Annoying Sound: In place of an in game chat between the two players, heroes are given 6 emotes they can use at any time: Greetings, Sorry, Well Played, Threaten, Oops, and Thank You. Not a bad idea, as a chat would have allowed players to express their frustrations to each other in unpleasantways, but because of how the voice acting was executed, the heroes come off as smug and sarcastic, which some players use to their advantage to rub a loss in in their opponents face, like saying Sorry or Greetings when finishing off the opponent. Heck, a common joke (and for some, the truth) is that the characters who sound the most sincere in their "Sorry" emotes are Uther and Lord Jaraxxus.
Lord Jaraxxus:You face Jaraxxus, Eredar lord of the Burning Legion!
Scrappy Mechanic: The sheer amount of random effects in the game can drive players insane. For example, Multi-Shot deals 3 damage to 2 random enemy minions, so if your opponent already has a cluttered board, it can be a crapshoot whether you actually deal damage to what you need to deal damage to. Another example is Doomguard, an extremely powerful minion but it forces you to discard two random cards upon summoning it, and you can just kiss your best cards goodbye because you don't get to choose what cards to discard. Warlock players got around this with the "Zoo Deck," which fills their deck with cheap but effective minions and spells which makes losing two of them much less of an issue.
“Stop Having Fun” Guys: Like many games with a competitive "eSports" scene, the lower echelons of Hearthstone's Ranked mode are dominated by people who the metagame doesn't affect, who insist you should follow it anyway. The Meta doesn't really start applying until the upper teens in ranked mode, at the very earliest. This isn't to say following some common wisdom can't make you a better player, but rather, that some take this far too seriously.
That One Boss: The Paladin class challenge against Kel'Thuzad is crazy hard by the standards of non-heroic Naxxramas, for all the wrong reasons. The idea behind the deck given to the player is to use the various, cheap buffs to power up a large swarm of small minions. Only 2 minions (Cultmaster and the Black Knight) have more than 3 attack, resulting in a dependency on buffs, despite the fact that the deck has very few of them. This results in the player often having a large board of minions with very low attack and health; Kel'Thuzad on the other hand has decently powerful minions that force extremely poor trades and can kill the player fairly fast, not to mention his access to the Twisting Nethernote Destroy all minions on the board spell. The fight boils down to hoping Kel'Thuzad doesn't get any good cards while the player has to hope they get theirs, which goes against the point of the challenges being examples of fun strategies. This fight became notorious for its difficulty on launch day, and even Legend ranked players have required multiple tries.
That One Sidequest: "Class A or Class B Dominance" daily quests (example: Druid or Hunter Dominance) are probably among the most aggravating and boring quests. They ask you to use either Class A or Class B and win five matches with them, and completing them gives you 60 Gold, averaging at 12 Gold per win. "Class A or Class B Victory" quests, another kind of daily quests, give you 40 Gold for winning just TWO matches, thus 20 Gold per win, making Dominance quests worth so much less for far more hassle. Woe to you if you keep getting Dominance quests that require entirely different classes to complete multiple days in a row, as they will SAP your time simply trying to complete those dailies. And while the game gives you an option to replace a quest you don't want, the replacement is just as random; you may end up losing a Dominance quest for ANOTHER Dominance quest.
On the other hand, the amount of gold that you can get per day is limitednote 100 from matches + whatever you can get from quests + whatever arena rewards you get.. Having dominance quests thus allows for more gold per day, which means more packs or arena runs. Dominance quests is actually favored by Arena-only players because the quest alone contributes more than a third of the entry price to said arenas.
Tier-Induced Scrappy: Valeera the Rogue was considered THE overpowered class by quite a few players. Averted now, since she's been nerfed to the ground, although players still complain about Miracle Roguenote Uses Gadgetzan Auctioneer and 0-cost spells to draw most of the deck, then plays an almost one-turn kill combo with Leeroy Jenkins or a combination of Malygos and damaging spells..
On the other end, there's a reason why Garrosh is one of the least played characters, outside of his ludicrously expensive Control deck where all or almost all of his minions are Legendaries.
The Priest, as well, with many players stating they'll flat out concede to a Priest just to avoid playing against one. When they were nerfed to low tier, they still weren't very fun to play against and tended to drag games out inordinately long.
Shadowform and Mind Blast are almost never used due to basically trying to make the Priest a Mage that isn't as good at its job, and Shadowform's effect can basically be accomplished by the Auchenai Soulpriest, which you can remove if you don't want its effect anymore. Although most people never expect a Velen-boosted Mind Blast to the face, so there is shock value, if nothing else.
A nerf to Mind Control has brought some of the heat off Priests. This led to Mages dominating tournaments, getting the ire of the community until they received nerfs of their own.
Then Mages' freezing mechanic was nerfed, leaving aggro-heavy Warlock builds to run rampant.
Hunters once dominated the meta game when Unleash the Hounds was reduced in cost from 4 mana to 2. While the card is still a very effective combo piece and a cornerstone of most Hunter decks, the cost increase to 3 mana has made it significantly less overpowered. But now people are already seeing a massive resurgence of Hunters, and some of the flat out amazing cards they received from the Goblin and Gnomes expansion do not look like they're going to make Hunters any less prevalent.
Many players dread the cry of LEEEEEROY JENKINS! for he is usually played as the last thing they hear before they lose. He is an extremely efficient Charger at 6 attack for 4 mana and his supposed drawback, summoning 2 1/1 Whelps to the opponent's side of the field, can be made inconsequential by either using him as a finisher or using an Area of Effect spell against the Whelps. Also, he can be comboed for ridiculous amounts of damage, such as with the aforementioned Miracle Rogue. It was so easy for people to win in one turn with Leeroy that his mana cost was later increased up to 5 to make him more manageable to deal with.
In terms of cards, Kel'Thuzad. Acquiring him isn't random (you are guaranteed to get him if you finish the Naxxramus single player adventure, which you more or less must buy your way into), his attack (6) puts him just below the range of Big Game Hunter, and his effect will usually win the game for his controller unless he's dealt with immediately. Advice: if you're up against a Deathrattle deck, save that Polymorph card.