Hearthpwn

Here's my idea ( look, i'm even typing correctly for once so people don't get mad at me ) you can use any class card for any class. for example, as a hunter, you can play druid, priest, warrior and shaman cards in one deck, if its too chaotic, we can always have it so there's a limit to however many different classes you can have per deck. for example, using only 3 different types of class cards in deck at max ( so, 3 classes' cards, not 3 class cards )

Mysterious challenger in mage, as a 1 of already too insane, same for any good aoe in rogue or hard removal in druid.

Raza in Mage would also be insane, as it then combos with Coldara Drake. Or just put all the Jade cards from Rogue, Shaman, and Druid in one deck. Or combine the Hunter and Druid beast cards. 0_o

I'm sure there are many examples of broken interactions. The game is not designed with intermixing of classes in mind.

Forbidden Healing and Embrace the Shadow.

The thing is though, that Tavern Brawls should be chaotic and all, there wouldnt be just one good deck because of all the good cards to synergize with. Just my two cents though.