Magister Kalendris

West: gardens and upper halls
Clear the trees around Tendris before engaging him, then work through the upper halls. Clear the guardians around each pylon along the way; defeating the named enemies alone does not open Immol'thar's prison. Tsu'zee is an optional rare encounter in the halls, not a required stop before the prison.

Magister Kalendris
Elite UndeadKalendris's Shadowform strengthens Shadow damage while reducing incoming melee damage, so interrupting Mind Flay matters more than forcing melee damage through the form.
Abilities

Shadowform
Assumes a Shadowform, increasing Shadow damage dealt by 40% and reducing melee damage taken by 40%. Shadowform lasts until cancelled.
Expect stronger Shadow attacks and reduced melee effectiveness during Shadowform. Keep interrupts available instead of trying to offset the form only with more melee attacks.

Mind Flay
Inflicts Shadow damage to an enemy and reduces its movement speed for 3 seconds.
Interrupt Mind Flay to end its Shadow-damage channel and movement reduction.

Shadow Word: Pain
Utters a word of darkness, inflicting Shadow damage to an enemy every 3 sec. for 18 seconds.
Remove Shadow Word: Pain as a magic debuff before its repeated damage overlaps another Shadow attack.

Mind Blast
Inflicts Shadow damage to an enemy, but causes a high amount of threat.
Use an available interrupt on Mind Blast when the tank is already low, but retain coverage for the next Mind Flay.
Tank- Keep Kalendris in the cleared hall with melee interrupts in reach. Use a defensive response when Shadowform overlaps an uninterrupted Shadow cast rather than advancing into the next pack.
Healer- Remove Shadow Word: Pain and prepare for increased Shadow damage during Shadowform. Keep the slowed Mind Flay victim in range while an interrupter ends the channel.
Damage- Coordinate Mind Flay interrupts. Spell damage avoids Shadowform's melee reduction; melee players should preserve their interrupts even when their attacks are less effective.