Considering that the main claim to fame for Leeroy Jenkins is running head first into battle by himself like an idiot, it seems odd that he's mostly just a Charge minion who waits patiently in in your hand until you play him. Then you realize that while he's in your hand, he's AFK like in the first part of the video.
A similar note applies to Grommash Hellscream. Why does the furious berserker sit in your hand? Well, think about where his summon quote ("I can wait no longer!") is taken from - a mission in Warcraft III where he attacks human encampments. At the start of said mission, Thrall orders him to leave the humans alone, and he does so for some time before finally uttering those words and attacking. While he's in your hand, he's restraining himself until finally he can't hold back the bloodlust any longer and has to fight.
Ragnaros, the Lord of the Firelands, shows up with 8 health. He's the (level 60) Molten Core version, not the (level 85) Firelands one.
A possibly unintentional example with Lady Liadrin, the alternate paladin hero, who summons Uther's Silver Hand recruits with her hero power instead of her own Blood Knights. This seems — and probably was — simply an unimportant technical aspect of the paladin deck that wasn't worth changing. Come World of Warcraft: Legion, though, Liadrin actually is a supporting leader of the reformed Silver Hand.
Pretty much everything regarding the Old Gods:
In canon, they don't exactly get along, to the point of being at direct war with each other. Suitably, their cards are physically incapable of working together: Y'Shaarj would negate the battlecries of the other three, Yogg-Saron thrives in a spell-based deck while the others require powerful minions, N'Zoth can't re-summon them with his battlecry, and C'Thun has very specific deckbuilding requirements that can't accomodate the other Old Gods.note You actually can make a pretty good deck that uses C'thun, N'zoth, and Yogg. It just isn't very consistent.
In Warcraft lore, Deathwing came about from the nefarious whispers of the Old Gods afflicting the poor Neltharion in his slumber, with N'Zoth at the forefront of his corruption. Whispers of the Old Gods adds an alternate version of Deathwing called Deathwing, Dragonlord whom boasts the powerful deathrattle of summoning all dragons in his owner's hand. Because he has a deathrattle, Deathwing D. can be summoned by N'Zoth.
Unlike his brethren, Yogg-Saron has no followers, instead contenting himself to simply drive his jailers in Ulduar to madness. In Hearthstone, Yogg-Saron is the only old god who does not require minions to activate his abilities, instead demanding spells.
The playstyle of a C'Thun deck is about emulating a Cosmic Horror Story. The deck starts with the standard cultists, who while threatening are still normal and understandable, but every time one of them buffs C'Thun, your opponent is given a glimpse of the horror behind them. As C'Thun gets more and more powerful, he starts whispering whenever he's buffed, ramping up the dread until finally you play him. You can even imagine defeating your opponent with C'Thun as them going insane from seeing the Eldritch Abomination in his full glory, just like a Lovecraft protagonist.
Some people questioned how Paladins could get involved in Mean Streets of Gadgetzan, as Paladins are noble forces who stand for justice. However, some of the Paladin cards seem to take on the more "legitimate business" side of things.note Grimestreet Outfitter is a tailor and Grimestreet Protector appears to be a defense attorney. Maybe the whole reason the Grimy Goons recruited some Paladins is because nobody would suspect them. Paladins can't be crooks, these guys must be on the up and up!
On another note, Gadgetzan, being Gadgetzan, has no actual law enforcement except SergeantSally, siding with the "Men of the city" would be the lesser of the three evils compared to the two very psychotic and sinister organizations whose nefarious goals mean nothing good, would be the best option.
In Knights of the Frozen Throne, Hunters got Professor Putricide as a Legendary, with the effect of creating and playing a random Secret whenever you play a Secret. A lot of people noted that the character had nothing to do with Hunters, and that the effect had nothing to do with the character. However, that's not the case. In World of Warcraft, Putricide had two pets; Festergut and Rotface, who were stitched together from various animals. This exactly like Deathstalker Rexxar's hero power. As for his ability, what other minion put secrets directly into the battlefield and was popular in Hunter?
As described in the Tier Induced Scrappy page, Freeze Mage has been a very consistently despised deck archetype since Hearthstone's beta. Of course Jaina would be the perfect poster girl for the Evil Is Deathly Cold Frozen Throne expansion.
Mage: The True Lich, which sets your health to 1. Mages typically use spells to damage their opponent, and by putting them at a dangerous situation they have no choice but to dish out every spell they can use out of desperation. If you don't prepare for the Lich King's onslaught, you'll be toast.
Shaman: Spirit Echo, which sets the stats of every minion in your possession to 1/1. The Shaman's main niche involves filling the board with minions that support each other, but what better way to ruin it by dismantling the Shaman's strategy by decimating their minions?
Hunter: The Hunted, which damages you for all of the minions in your deck. Hunters are known for going all-out with lots of battle-ready minions, but The Hunted restricts you from doing so. Instead, you must rely on secrets and minion-summoning spells to fill your board.
Druid: Purge The Weak, which removes all of your minions that cost 3 or less, including the ones in your deck. Druids are known for having the ability to ramp Mana Crystals and getting lots of expensive cards to compensate. With the Lich King barring your ability to play cheap minions, you must ramp in order to stand a chance.
Paladin: Fallen Champions, which allows him to take control of your minions when they're defeated. Paladins rely on summoning minions (and their Hero Power even relies on summoning minions), but the Lich King is able to wrench control away by turning the power of your own minions against you.
Rogue: The Price of Power, which removes every spell that you have. Rogues rely on spells to gain control such as dealing direct damage, buffing their units and stealing their opponent's cards, so the Lich King removed the Rogue's ability to gain the upper hand. You'll only have to rely on minions who must fight on their own.
Priest: "Shut Up, Priest", which muffles your emotes. The Priest class is considered to be the weakest of all of the classes, relying on healing and copying the opponent's card in order to be useful. The Lich King must have thought that the Priest class was Not Worth Killing due to its weakness, so he left the gameplay as normal. However, emotes are considered to be a different story to the gameplay itself as it can be used to directly annoy the opposing player, so the Lich King muted Anduin's emotes to make him both helpless and BM-less.
The Mark of Hakkar card back is obtained by playing against another player with that very card back. This means that its availability spreads like an infection — much like the Corrupted Blood pandemic that Hakkar accidentally caused in World of Warcraft.
Take a closer look at Cabal Shadow Priest's artwork. Now compare it with Northshire Cleric's. Did you notice they both have black hair and wear the same clothings? Sure they may not be the same person, but at the very least they are from the same order. And the Cabal Shadow Priest's flavor text makes it all the more chilling.
Cabal Shadow Priest: You never know who may be secretly working for the Cabal....
If the Inn can travel through space and time and the Innkeeper can control this... well, let's say that prospect of getting thrown off the tavern sounds way less pleasant than usual. That may be the reason why everyone play nice, though - since being kicked out means you're now stuck wherever the inn is placed. You might have entered the inn to take shelter from the Whispers of the Old Gods, and get kicked out in Un'goro with no way home.
The Doppelgangster is a 2/2 Dwarf who summons 2 more 2/2 minions as a Battlecry. But considering his very unusual appearance (purple skin) and the minions he summoned are Faceless Ones, it's very likely that the 'Dwarf' is a Faceless himself. Another is the Darkshire Councilman; when you look closer at his shadow, they're very tentacle-y. What's particularly chilling is that Faceless Ones are usually found underground, or close to areas with significant Old Gods' presence. But these 2 cards showed that the Faceless Ones have started to infiltrate local organizations...
The Kobold's You No Take Candle is a memetic Running Gag. But come Dungeon Run mode, and you find out exactly why they insist you don't take any candles. In fact, when the relevant card is in play, you will hope you don't take any candle.
There's a reason to always keep a light on down here.
Floop's glorious gloop is a funny spell name, as befits the quirky botanist, and the bright, cheery colors make it easy to overlook the more sinister undertones. Then you take a closer look at how he works, and what the spell exactly does: one extra mana for each minion dying this turn. They're being used as fertilizer.