Is this a new exploit in the system?

Brann + Illucia will do nothing but will revert the deck and hand with opponent on your next turn, giving your opponent a useless deck till the end of the duel. It should work and I don't think this is tested.

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Try running the Deathrattle package with this combo likethe Togg version.

You'll get to draw faster and give your opponent a deck that only draws, instead of a deck full of removals for your new cards.

But that will also at very least give them a turn with their own cards and deck, so they can react appropriately like playing togwaggle, leaving you with your own deck but not with the means to change it back.

That is, if you're not already dead before next turn arrives.

Or would it swap back twice because you triggered the battlecry twice?

there are a lot of removals there. The combo is 5 mana so you can even heal yourself with a greater healing potion for example. Priest in wild doesn't need minions to survive

Quote From nandop2000

Or would it swap back twice because you triggered the battlecry twice?

maybe, I don't think so though. Will have to test it.