Hearthpwn

Greetings :-)

Here is the deck I used to defeat to defeat Terestian Illhoof in heroic mode. I won during the first attempt.

For this boss, I propose you this free to play (F2P) deck. The only drawback is that it contains some wild cards, but I think you could replace them.

Overview of the boss

Terestian floods the board with 2/2 imps that revives once killed. The only way to damage him is to kill his daemon.

Since Terestian has a lot of HP and immortal army, we basically must defend as much as possible.

Overview of the deck

Taunt minions is the best way to save your own HP and guarantee that Terestian Illhoof will empale his daemons and get damage. To this end, we put many good taunt minions (Tar Creeper, Lone Champion, Tortollan Shellraiser).

We want to boost them with Power Word: Shield and Divine Spirit, or at least heal them (Lightwell, Divine Hymn, Greater Healing Potion).

We also include as most as possible AoE (Holy Nova, Duskbreaker, Primordial Drake), because it will be a huge source of damage. Note that dragons are perfect to get AoE and big taunts.

Strategy

• Mid game: build a big taunt with Divine Spirit and heal it. All your cards with cost lower than 4 are here to survive until the late game.
• Late game: let Terestian empale his minion on your big dragons. Cast your AoE when there are many daemons on the board. In practice you will kill the boss very fast. If there are 5 imps, you deal 10 damages per AoE, and Terestian loose 10HP per turn when he empales his minions. So if you reach the late game, you should have big dragons in hand and thus win...

Tricks

• Ideally, cast Mass Dispell before an AoE to disable imp's deathrattle. Then you'll kill them definitely.
• If you cast Power Word: Shield and Divine Spirit on the same minion, try to play them in this order to maximize its HP.
• Remember that the boss has some spell like Corruptionable to kill your minions. So avoid to cast all your spells one the same minion.

Mulligan

• Power words: shield
• Divine Spirit
• Small taunts (Lone Champion, Tar Creeper, ...)

Obviously, dragons and AoE are for the late game, so you should discard them.

Replacements

• About obsolete cards: I only used Greater Healing Potion to save a Tortollan Shellraiser boosted by Power Word: Shield and Divine Spirit.
• About epic cards to be honest Primordial Drake is a strong card, so it is a good card to craft.
• Shadow Visions is also a very good card, so you should also craft them if you play priest. It allows to play more than twice the same spell in the same game and give you more flexibility depending on the threats. But I guess that you should be still able to win by replacing them by cards in the spirit of the deck (taunts, AoE...)

I hope you will enjoy this deck and that it will help you to defeat this boss. If so, do not hesitate to upvote the decklist!

Good luck!