Thrall Boss Guide for Book of Heroes (Jaina)

Thrall uses a deck comprised of fairly standard Shaman cards, such as Feral Spirit and Fire Elemental in addition to some Horde-themed cards like Frostwolf Warlord. He uses the Spirit of Air Hero Power on his minion if any are left alive on the board.

For the encounter you will be given a similar Dragon Mage deck to the one used to fight against Garrosh Hellscream. However, you will receive the Icefall Hero Power to support your board.

In your mulligan, you are largely looking for Frostbolt and Scalerider to help control the board in the early game. Additionally, you can keep the Focusing Iris card due to its sheer power in the late game.

In the early game you should focus on preventing the board from keeping any minion on the board. This can be done with cards like Frostbolt. From Turn 3 onward, this can be done using your Icefall Hero Power which, even if it does not immediately kill a minion, can still Freeze them so that they can be killed on the following turn. With the board under control, you should begin to develop the board with your large Dragons. However, you should prioritise playing Twilight Drake much less due to the boss's use of Earth Shock.

Developing the board and controlling it from the mid game onward is often enough to win the game. You can also try to play Focusing Iris in the late game. This will give you a full board of Water Elementals, which may just win the game for you. However, you should not rely solely on this card as boss runs one card specifically, Earthquake, that can deal with it.