Fake card time. The Scarlet Monastery was one of my favourite WoW instances back when it was new, and it's still okay even though they've re-designed the whole thing twice (???) for no apparent reason. I don't think there are any Scarlet Crusade cards except for that Paladin GvG card that does two damage to all minions with Deathrattle, and totally failed to see any use because Undertaker was nerfed and Deathrattle decks aren't consistent or popular enough.
A problem with releasing Scarlet Monastery cards is how limited they'd be in classes. Either you would have to make them all neutral cards, which severely limits how cool effects the legendaries could have, or the only classes that would get class cards based on the real instance would be Paladin, Priest, Warrior and maybe Hunter. Maybe you'd have to turn it into a Stratholme pack so the other classes could get some representation from the undead bosses.
Priest card because Mograine would obviously be a Paladin card. Rivendare stats for the same mana as Rivendare. For this card to be useful, the Scarlet Monastery expansion would probably also have to add some big taunt minions without Divine Shield so you wouldn't have to rely on Mind Controlling an enemy Tirion Fordring.
Deathlord with an arguably positive effect for way more mana, but also means you can't use Silver Hand Recruits while he's out. I can't tell if this effect is way too good or slightly too bad. Yes, the intent is that it kills buffed 3/3 or 5/5 dudes too, and your opponent's dudes as well.
Herod would be a Warrior Legendary and that guy with the dogs would probably be a Hunter card.
Fake edit: Bloodmage Thalnos is absolutely a Scarlet Monastery card. Forgot about him.