Hearthpwn

 My v1 Hakkar Priest Control Deck

https://www.hearthpwn.com/decks/1212271-hakkar-plague-a-priest-control-deck

The best hand usually starts with:
Dead Ringer with Power Word: Shield and Awaken the Makers that is always on starter hand.

Other combinations can be with Radiant Elemental, Power Word: Shield and Lesser Diamond Spellstone with a coin.

Turn 1: Coin +  Radiant Elemental and Power Word: Shield and Awaken the Makers.

You buy 1 card, place a 2/5, start the quest, and Lesser Diamond Spellstone is only 1 to complete the first level.

Against classes that are playing more aggressively hold at least one Mass Hysteria  in hand. Use Twilight's Call as long as you have killed two minions with deathrattle. The faster you can complete Awaken the Makers the better. With 7 mana you can already play Amara, Warden of Hope and Seance. It's even better to have an Spirit of the Dead on the field to ensure Amara returns to the deck.

Use Lyra the Sunshard to take advantage of the game. Remember to use the coin and Radiant Elemental to use Zerek's Cloning Gallery as fast as possible.

You can win with Hakkar, the Soulflayer but you can also control the game and cause a lot of damage to your opponent even before he buys the first Corrupted Blood.

Keep more cards than your opponent on the deck: Spirit of the Dead with Zerek's Cloning Gallery and Lesser Diamond Spellstone. Decks like paladin, rougue, mage, warlock and shaman buy many cards and this is great. Deck combo like Tiger TTK are little useful against this deck because of that.

The game complicates Mage and Shaman. With cards like Hex and Polymorph the Hakkar is useless. With this situation, the solution is you put the Hakkar and the same turn destroy. It is only possible with Coffin Crasher or Zerek's Cloning Gallery (if it is already in the field and you use Shadow Word: Death or Shadowreaper Anduin or switch with another opponent's minion).

You can exchange Mass Hysteria for Psychic Scream but I recommend playing with only one on the deck.

Up to 2x Rotten Applebaum instead of Zilliax and Coffin Crasher.

Awaken the Makers should not be replaced however recommend the first version of this deck.

I have not found any other better substitutions yet I accept suggestions.

In general you should always: Dead Ringer and Gilded Gargoyle or Radiant Elemental and Power Word: Shield.

Against aggressive decks:
(Odd Paladin, Spell Hunter, Secret Hunter, Zoo Warlock and Even Warlock)
Dead Ringer with Spirit of the Dead in the second round (with coin) is an excellent option. You can keep Spirit of the Dead longer in the field with Power Word: Shield when it's too hard to take it off. In specific cases (Odd Paladin and Zoo Warlock) it may be good to try to hold an Mass Hysteria for turn 5. Against Secret Hunter always keep a Shadow Word: Pain on hand to avoid Secretkeeper.

OTK DK Paladin
It is usually very easy to win from this deck. You keep track of the field and fill the opposing deck with corrupted blood. Best of all: your opponent buys many cards during the game.

Spell Hunter
This case is very specific because it usually creates a difficulty controlling the field when the opponent can play some Lesser Emerald Spellstone. Mass Hysteria may not be enough. If you are facing several of these in your rank I recommend trading an Shadow Word: Death for Psychic Scream. It can be more effective and this will end the effect of Rhok'delar. In addition Zul'jin becomes dangerous because trigger Corrupted Blood (for your opponent).

Druid
(Undatakah and Taunt)
Here you need to finish your quest as fast as possible. Twilight's Call is excellent and if possible use Lesser Diamond Spellstone before turn 7. After that the game is basically controlling and helping your opponent to buy Corrupted Blood. Lyra the Sunshard usually helps a lot to control the field. Remember that Obsidian Statue is an excellent defense. Usually the game is 50/50.

MECHA'THUN DRUID
It's your game. Whenever possible add more and more corrupted blood on the opponent's deck (and yours). But create strong pressure with Zerek's Cloning Gallery and Lesser Diamond Spellstone.

Mage
(All current)
Okay. Here's a little more complicated. All wizard options end up giving a huge damage in a few turns. The ideal is to keep the field under control at all times. The most valuable starting hand is Spirit of the Dead and Dead Ringer and the first purchase an Power Word: Shield helps a lot. Take care of Polymorph. You can completely ruin your move with Hakkar. Always use Coffin Crasher with a trigger for Hakkar and if possible destroy it before your opponent turns into a sheep.

SHUDDERWOCK SHAMAN
Another deck to take care of with Hex as well as Polymorph. Earth Shock is not as effective since you can revive the Hakkar but it is important to break the purchase of cards with Corrupted Blood. Here you should seek a more aggressive field and do a lot of damage with your minions. The default hand (at the beginning of this topic) is the best option. Complete the quest as soon as possible.