Get an honorable, killing blow on one of each class.

That Takes Class

Defeat the Conclave of Wind in the Throne of the Four Winds on Heroic Difficulty.

Heroic: Conclave of Wind

Defeat Cho'gall in the Bastion of Twilight on Heroic Difficulty.

Defeat Valiona and Theralion in the Bastion of Twilight on Heroic Difficulty.

Defeat Halfus Wyrmbreaker in the Bastion of Twilight on Heroic Difficulty.

Defeat Maloriak in Blackwing Descent on Heroic Difficulty.