Defense Control Crystals are found on the walls in Violet Hold. When activated, they will kill most mobs in the room, with the obvious exception of bosses. As the guards leave when the instance is started, they activate a crystal to kill the remaining invaders.
- There are a total of six crystals in the room, but one of them is used by before she leaves the Hold, leaving only five available to the players. Each crystal can be used only once.
- They are especially useful against the Ichor Globules in the Ichoron fight, when trying to get the achievement.
- One of the objectives of the achievement is to complete the instance without activating any crystals. Most sufficiently geared groups should have no problem doing this.
- Activating a crystal will hit each mob with Arcane Lightning for 13000 Arcane damage on normal difficulty.
- In the beta-test version, this feature was implemented as an item that was given to players. See Defense Control Crystal (item). They are now objects at fixed locations in the room.
- Originally there was a cast time of a few seconds for the Crystals. This has been removed, and the activation is now instantaneous.