Treachery Combos I've been contemplating:
Bittertide --> (next turn) Treachery + Spreading Madness + Spreading Madness/Defile/Mortal Coil
Apothecary + Treachery + Dirty Rat + Dirty Rat
Obviously Doomsayer & Ticking Abom
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Rogue DK seems good to me, can slot into the Arcane Giant list pretty easily I think.
You can mimic a ton of Rogue stuff very easily, even copying coins can be valueable...
I don't see how it isn't played tbh. 9 Mana is expensive but it's extremely powerful.
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Edit: 9 mana rogue uses DK and grabs a copy of Shadow Reflection (shouldn't unstealth hero I think?)
Next turn: Auctioneer + Coin + Shadow Reflect Coin + HP + Shadow Reflect Coin + Van Cleef (10/10) + 4 mana remaining still
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Edit2: Blizzard says Shadow Reflection leaves your hand at end of turn, so no way to use 2x in a turn, and can't use on cards over 5 mana (easily)