Azari, the Devourer's hero power is Devour. This is his deck. One more card should probably only have one copy - perhaps Demonwrath or Bane of Doom. I thought it was Doom!, but there are two of those.
King Togwaggle's hero power is Magic Candle which generates a random playable dungeon run treasure (no passive treasures such as Captured Flag). Like the other final bosses he starts his first turn on 3 mana. Here's his deck.
That is the intended function, just like Baron Rivendare and Weasel Tunneler, Malorne, and in some sense Sherazin, Corpse Flower. These deathrattles act on the cards themselves, not copies - there is no second card to return to your hand, or to deck, etc.
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Azari, the Devourer's hero power is Devour. This is his deck. One more card should probably only have one copy - perhaps Demonwrath or Bane of Doom. I thought it was Doom!, but there are two of those.
1x Mal'Ganis
2x Abyssal Enforcer
2x Bane of Doom
2x Demonwrath
2x Despicable Dreadlord
2x DOOM!
2x Doomguard
2x Dread Infernal
2x Dreadsteed
2x Fearsome Doomguard
2x Flame Imp
2x Kabal Trafficker
2x Pit Lord
2x Voidcaller
2x Voidlord
2x Wrathguard
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The Darkness's hero power is Encroaching Darkness. He begins his first turn with 3 mana. You start the fight with 3xLuminous Candles.
This is his deck.
1x Potion of Madness
2x Cabal Shadow Priest
2x Entomb
2x Evasion
2x Forbidden Shaping
2x Mind Control
2x Psychic Scream
2x Shadow Bolt
2x Shadow Word: Death
2x Shadow Word: Pain
2x Shadowfiend
2x Sudden Betrayal
2x Twisting Nether
3x Looming Presence
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Vustrasz the Ancient's hero power is Vindictive Breath. Here's his deck.
1x Wrathion
1x Ysera
2x Azure Drake
2x Blackwing Corruptor
2x Chromatic Dragonkin
2x Cobalt Scalebane
2x Drakonid Operative
2x Hoarding Dragon
2x Holy Nova
2x Lightbomb
2x Looming Presence
2x Power Word: Tentacles
2x Spirit Lash
2x Twilight Whelp
2x Unidentified Elixir
2x Velen's Chosen
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King Togwaggle's hero power is Magic Candle which generates a random playable dungeon run treasure (no passive treasures such as Captured Flag). Like the other final bosses he starts his first turn on 3 mana. Here's his deck.
2x Rakanishu (these may not be in his deck, but occasionally occurs)
2x Backstab
2x Beneath the Grounds
2x Evasion
2x Eviscerate
2x Evolved Kobold
2x Kobold Apprentice
2x Kobold Barbarian
2x Kobold Geomancer
2x Kobold Hermit
2x Kobold Illusionist
2x Kobold Monk
2x Sudden Betrayal
2x Tomb Pillager
2x Vanish
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Bristlesnarl's hero power is Hunter's Call. Here's 28 cards in his deck. He wouldn't cast the other two even into fatigue.
1x Corpse Widow
1x Gahz'rilla
1x Giant Mastodon
1x Kathrena Winterwisp
1x King Krush
1x Swamp King Dred
2x Call of the Wild
2x Charged Devilsaur
2x Deadly Shot
2x Giant Sand Worm
2x Gladiator's Longbow
2x Kill Command
2x King of Beasts
2x King's Elekk
2x Savannah Highmane
2x Starving Buzzard
2x Tundra Rhino
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Lava-Filled Chamber's hero power is The Floor is Lava. If it overkills a 1 health minion, Explosive Runes will deal 7 damage to your hero. Here's his deck.
1x Kalimos, Primal Lord
1x Ragnaros the Firelord
2x Explosive Runes
2x Fire Elemental
2x Fire Plume Phoenix
2x Fireball
2x Fireguard Destroyer
2x Firelands Portal
2x Flame Geyser
2x Flamestrike
2x Forbidden Flame
2x Lava Burst
2x Lava Shock
2x Pyroblast
2x Volcanic Potion
2x Volcano
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Gutmook's hero power is Metabolized Magic. This is his deck.
1x King Mukla
1x Millhouse Manastorm
1x Troggzor the Earthinator
1x Volcano
2x Ancestral Knowledge
2x Burgly Bully
2x Burly Rockjaw Trogg
2x Crushing Hand
2x Flamewreathed Faceless
2x Gluttonous Trogg
2x Hoarding Dragon
2x Lava Shock
2x Lightning Storm
2x Snowfury Giant
2x Stormforged Axe
2x Totem Golem
2x Tunnel Trogg
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Xol the Unscathed's hero power is Beam Me Up!, which generates one of these cards depending on her emote.
Fatality - Beam of Death
Fatigue - Beam of Decay
Fear - Beam of Fear
Flame - Beam of Fire
Flummox - Beam of Confusion
Frost - Beam of Frost
She starts her first turn at 3 mana like the other final bosses. Here is her deck.
1x Blood-Queen Lana'thel
1x Clutchmother Zavas
1x Deathwing
1x Lakkari Sacrifice
2x Cataclysm
2x Corrupting Mist
2x Dark Bargain
2x Darkshire Librarian
2x Despicable Dreadlord
2x Doomguard
2x Flame Imp
2x Lakkari Felhound
2x Malchezaar's Imp
2x Silverware Golem
2x Soulfire
4x Howlfiend
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Generated by Ixlid's hero power Sprouting Spore.
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That is the intended function, just like Baron Rivendare and Weasel Tunneler, Malorne, and in some sense Sherazin, Corpse Flower. These deathrattles act on the cards themselves, not copies - there is no second card to return to your hand, or to deck, etc.