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. Lest we forget that upon summoning, he drops his famous quote...
Lord Jaraxxus: YOU FACE JARAXXUS, EREDAR LORD OF THE BURNING LEGION!
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!
Baron Rivendare got tons of love straight from his reveal thanks to his ability to cause deathrattles to trigger twice encouraging creative strategies. It helps that he was the first legendary Naxxramas card revealed and that his boss fight is one of the more unique.
Fan Nickname: You will be hard pressed to find a player who refers to Sen'jin Shieldmasta by his actual name instead of his summoning emote "Taz'dingo!"
Also popular is calling the Knife Juggler as the "Knife Juggalo"
Noble Sacrifice frequently gets referred to as Get Down!!!
Defias Ringleader gets called the "Scrublord" due to being a cheap (yet very effective) card that summons another minion (when combo'd) as well as his memorable summoning quote; "This is our town, scrub."
The Savannah Highmain, a Hunter lion minion, is often called "Scar". He even summons hyenas when he dies!
Game Breaker: Husky Starcraft and his friend Sinvicta discovered that, using "Divine Spirit"snote "Double a minion's Health" and Lorewalker Cho, who has the odd effect of adding a copy of any just-cast spell to your opponent's hand, you can very easily get a Minion up above 1 billion health. Add an "Inner Fire"note "Change a minion's Attack to be equal to its Health and you have a very dangerous Minion. However, the utility of trick is limited, as it requires the two opponents to work together.
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 deals 10 damage to anything 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 as well be over, because there's nothing you can do to stop them from chucking a big, fat fireball at your face. Its mana cost was increased to 10 as a result.
The priest's Mind Control spell has similar, if less immediate effects: any high-value card played after the priest hits ten mana is mind-control bait, with every minion carrying the possibiity of being used aganst you. This was even worse before mind control was nerfed; now costing ten mana (and thus only playable at turn 10 and beyond, or possibly turn 9 if Anduin still has the coin), it used to cost eight.
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 a player didn't have silence to deal with it instantly, then they had, at minimum, a 6/6 running around rampant on turn 4, something nigh impossible to deal with without sinking a boatload of resources into killing it. Worse yet, they weren't legendary, meaning there could be 2 in the deck. It was later nerfed to a 4/1 that gains +1 health for every card in the hand, making it solid, but manageable.
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.
Scrappy Mechanic: The sheer amount of random effects in the game can drive players insane. For example, cards like Multi-shot aims at 2 random enemy minions, so if your opponent already has a cluttered board, pray that card will hit the minions you really, REALLY want to destroy. Or when you play Doomguard, it will randomly pick two cards in your hand and disposes of them, and you can just kiss your best cards goodbye because you don't get to choose what cards to discard.
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. This idea was taken too far- 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 Nether 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, even if doable. 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 is considered overpowered by quite a few players. Possibly 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. being a solitaire deck.
On the other end, there's a reason why Garrosh is one of the least played characters... though he's also a regular Scrappy so more than one reason.
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.
No one runs Shadow Priest. Shadowform and Mind Blast are almost never used due to basically trying to make the Priest a Mage that isn't as good at it's job, and Shadowform's effect can basically be accomplished by the Auchenai Soulpriest, which you can remove if you don't want it's 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.
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.
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.