Before anything, this is a theorycraft. No one knows how the future metagame will be shaped and if that kind of archetype will work. My goal is simply to share an idea in anticipation of the future KotFT expansion. So, please, don't come to me in few weeks to say : "Hey, it doesn't work !"... Thanks for your comprehension.

What is the gameplan of the Shadow Combo Priest ?

The objective of this deck is, first, to survive up to the late game thanks to board clearing spells. Then, either Prophet Velen or Malygos have to be summoned. There are many ways to achieve that : directly from the hand if there is no other choice, from Barnes and Shadow Essence if they are still waiting in the deck, or thanks to Eternal Servitude if one of them got destroyed. Once it's done, it only remains to use Holy Smite and Mind Blast to burst down the opponent in one turn. Another way to win, against agressive decks, is to exhaust them with several Obsidian Statue.

Are there other synergies ? What are the minions ?

Prophet Velen : He doesn't only double Holy Smite and Mind Blast damages, he also works with Dragonfire Potion, Spirit Lash (Deals 2/Heals 4 per minion), Holy Nova (Deals 4/Heals 4) and Voidform. In addition, he doubles the healing from Lesser Heal or Greater Healing Potion.

Malygos : He works with fewer spells but has a greater impact on them : Holy Smite, Mind Blast, Spirit Lash (Deals 6/Heals 6 per minions), Holy Nova (Deals 7/Heals 2) and Dragonfire Potion. It can be noted that the last one doesn't affect him since he's a dragon.

Bloodmage Thalnos : Same as above (except he does die on Dragonfire Potion). He can provide a better board clear and works especially well with Spirit Lash in early/mid game. The deck also needs to draw and that's why he fits, plus he's not that bad to get on Barnes' battlecry.

Barnes : Amazing to get an early Prophet Velen / Malygos / Obsidian Statue that can quickly be re-summoned with Eternal Servitude. He may also be used as a low-mana combo starter in late game. Getting Bloodmage Thalnos or Acolyte of Pain on him isn't bad since it cycles the deck.

Obsidian Statue : It combines a taunt, a heal and a big minion clear, which is exactly what is needed against aggressive decks. Exhausting them won't be hard because multiple copies of them can be summoned through Barnes, Eternal Servitude and Shadow Essence. Its deathrattle makes it, moreover, a solid choice also against control decks.

Acolyte of Pain : As drawing cards are needed in the deck, I prefered him over Northshire Cleric since he's better to get on Barnes, Shadow Essence and has a decent synergy with Spirit Lash (without needing a Circle of Healing). In addition, he's a great target for Power Word: Shield.

And what about the spells ?

Shadow Visions : One of the best Priest card at the moment. Its main purpose is to look for the right answer at the right moment, but it can also be used to provide another copy of important spells like Mind Blast, Eternal Servitude and Shadow Essence.

Dragonfire Potion : The biggest Priest's AoE that generally resets the board on Turn 6, as good in agressive matchups than in control ones. It doesn't affect Malygos, which can lead to a monstruous board clear if summonned through Eternal Servitude.

Greater Healing Potion : That one has already been proven useful in the previous metagame, mainly in Control Priest against Mage decks and agressive other ones. Its utility here is the same, it helps surviving and temporizing. In my opinion, it's a better card than Flash Heal because it's a more solid choice on Shadow Visions and it's insane with Prophet Velen. It can also be used on a very damaged Malygos, for example, restoring him to full health.

Shadow Essence : One of the card that brought me this archetype idea. Summon a copy of one of your huge minions (Prophet Velen / Malygos / Obsidian Statue) at a low cost, allowing sick combos. And if you happen to summon a 6-mana 5/5 Bloodmage Thalnos / Acolyte of Pain... Well, these aren't bad cards at all, it's okay to get them on it. This is very versatile!

Eternal Servitude : The second most important of the new cards (for this archetype) given by the Knight of the Frozen Throne. Basically, it makes summoning parts of your combos early-on totally fine, as it allows even bigger combos once resurrected. Plus, it's required in case you draw your parts near the beginning, and it has a nice synergy with Barnes. They definitely are necessary.

Spirit Lash : That card is totally underestimated. It's way too good against agressive decks as it will clear the low Health minions they usually play. Spell Damage can make it a decent board clear, but the most important feature of the card is the important heal it can bring. It's also a cheap activator to instantly draw a card with an Acolyte of Pain on the board.

Mind Blast : A dead card most of the game, that will also sound the death knell of the opponent.

Holy Smite : Even if that card is part of deadly combos, it has more versatility than its colleague. Against agressive decks, it can be used defensively to clear a minion at a low cost.

Holy Nova : Another AoE that helps surviving till the combos can be played. It synergies with the Spell Damage cards and it can deal some serious ones to the opponent Hero.

Power Word: Shield : Drawing is just too necessary. As you should always mulligan for your early minions, it shouldn't be too hard to play that card on them. At worst, it can be used on an opponent minion before playing a Shadow Word.

Shadow Word: Pain : Way too good in early game, whatever the matchup. That's a must-have.

Shadow Word: Death : The big game hunter, mandatory especially against Druids and Rogues. One exemplary should be enough, mainly because there is Shadowreaper Anduin in the deck.

Why Shadowreaper Anduin is present ?

His battlecry is great against most control decks or Jade Golem, while Voidform act as a finisher (especially with Prophet Velen) if the opponent built armor or didn't take enough damages from your minions. It comes on the same turn as The Lich King (among others) so he can be a great answer. I definitely think he's worth a slot, but it will depend on the metagame's pace.

ANDUIN THANKS YOU FOR READING !