Tyrant has the Epic Siege on Kor raid. The commander summons a Rat Catcher every turn, which can immobilize you and Phase you as well, blocking that unit from being affected by your own friendly activation skills. The core structure cards are some of the deadliest in the entire game, including the Cannon Wall, which has 15 health, and in 3 turns it Enfeebles all of your units, making them take 2 additional damage from all attacks and then proceeds to Strike all of them for 3 damage (after the effects of Enfeeble). There's also the Cluster Mine, which has Counter 10, which will pretty much kill any of your units that hit it. You think you can just Siege away those structures? Well, it also has two of its own version of the Gatling Tower, which will Strike one of your own units for 4 damage, inflict Chaos on all of your units, turning all of your own attack skills against yourself and thus blocking any Siege strategy you might employ, and Sieging all of your structures for 2 points of damage, all after only 2 turns. If that's not enough, the randomly generated player-available cards can make it even worse, including the Metalworks, the Usial, and Orwold's Reckoning, all of which can summon even more enemy units in addition to the commander's Rat Catchers. The best possible deck for this raid has only a 77% win rate, while all other raids have at least one deck with a 95%+ win rate, and it has 1.2 million health which requires great contribution from all 40 possible people to take it down within the 3-day time limit.
Hearthstone: Heroes of Warcraft has the Crone from the One Night at Karazhan adventure. Her fight's gimmick gives out some good news and bad news: the good news is that Dorothee can give your minions Taunt or Charge depending on where you place them; the bad news is that this is an Escort Mission with Dorothee at only 10 hit points as your escortee; if she dies, the Crone's Hero Power kicks in and gives you what's essentially a One-Hit Kill to your hero. Unfortunately, she has plenty of resources to whittle down Dorothee and your Taunt minions from Stealth minions, her exclusive Flying Monkeys with Charge and attack power that can easily land a killing blow to Dorothee, the dreaded Knife Juggler, and even Twisting Nether that destroys all minions (including Dorothee) on the field. Lord help you if you're playing on Heroic Mode, as on turn eight the Crone automatically draws Twisting Nether; have fun trying to deal 60 damage to her in eight turns.