Darkheart Thicket is a dungeon whose entrance is located in Val'Sharah on the continent of The Broken Isles in the World of Warcraft game. The minimum level for this dungeon is 100+. The dungeon contains 4 bosses. The end boss of Darkheart Thicket is Shade of Xavius.
Darkheart Thicket is the dungeon that you do at the very end of the Val'Sharah questline. The questline ends with you taking on the Shade of Xavius who has captured Malfurion Stormrage, druid husband of Priestess Tyrande Whisperwind and brother of Illidan Stormrage, the Burning Crusade expansion antagonist.
Throughout the end of the Val'Sharah questline, you helped Tyrande look for her husband and it all leads to here, a dungeon in the northern edge of the zone. The dungeon is populated with antagonists such as walking flowers, trees, corrupted bears and dragons.
For most of the battle, he'll remain in Night Elf mode but will on ocassions jump as a panther and attack a player far away. This will seem similar to the bosses in Zul'Aman, so long as your healers good, you shouldn't have too much to worry about.
Oakheart is a giant Nightmare tree that will create roots around the area of the fighting zone to trap the players. You need to keep moving and when a player has been caught, be ready to free them.
Dresaron, the nightmare dragon will fight mainly in one place if you can keep her there. Around the edge of the fighting area are eggs which when touch will crack open and a baby dragon come into fight. Dresaron will push you towards the the edge so you need to be ready to fight back against the push otherwise you will get adds. Its not easy to just ignore the adds, you need to take them out at the same time as taking on the boss.
In the final room, Malfurion will be entangled in roots at the far end. Malfurion will released himself on the death of the Shade so you won't have to do anything there. The boss is relatively easy, you can tank him on the spot. When he poisons the ground, just move out of the way, there is only one phase here. The actual Xavius is saved for the Emerald Nightmare raid which you will do when you're equiped or in a raid party for.