Balnazzar

Scarlet Bastion
Work through the Hall of Lights to Malor, then continue to Willey's cannon room and Galford's archive before the final chamber. Dathrohan's transformation begins the Balnazzar portion of that last fight, not the end of the branch. Blacksmithing Plans along the Bastion route can summon Crimson Hammersmith; treat the plans as an optional pull when encountered, not a required stop after Balnazzar.

Balnazzar
Grand Crusader DathrohanElite HumanoidElite DemonDathrohan's transformation extends the fight into Balnazzar's fear, sleep and mind control, so the party must preserve resources and control affected allies rather than damage them indiscriminately.
Abilities

Crusader's Hammer
Stuns nearby enemies, rendering them unable to move or attack for 4 seconds.
Crusader's Hammer stuns nearby enemies; keep the healing position away from Dathrohan and prepare tank health before the stun.

Crusader Strike
Crusader Strike increases the Holy damage its victim takes; expect the tank's Holy damage pressure to grow during Dathrohan's part of the fight.

Holy Strike
Holy Strike adds a Holy weapon hit, so armor alone does not cover the tank's incoming damage.

Balnazzar Transform
The transformation restores health and begins the demon fight. Keep resources for Balnazzar instead of stopping when Dathrohan is nearly defeated.

Mind Blast
Inflicts Shadow damage to an enemy, but causes a high amount of threat.
Keep Mind Blast's target healthy while the party recovers from the encounter's control effects.

Shadow Shock
Instantly lashes nearby enemies with dark magic, inflicting Shadow damage.
Shadow Shock hits nearby enemies; keep ranged players away from Balnazzar rather than adding them to the melee healing load.

Psychic Scream
Lets out a psychic scream, causing up to 5 nearby enemies to flee for 6 seconds.
Fight inside cleared space so Psychic Scream cannot send players into surviving Crimson enemies. Use available fear protection or removal for the healing position.

Sleep
Puts an enemy to sleep for up to 20 seconds. Any damage caused will awaken the target. Only one target can be asleep at a time.
Remove Sleep from the healer or the player assigned to control a mind-controlled ally when a magic dispel is available.

Mind Control
Use nonlethal crowd control on the mind-controlled teammate and stop attacks that would kill that player. Re-establish the boss target when control ends.
Tank- Keep Dathrohan's nearby stun away from the healer and retain a defensive for the Holy damage pressure. After transformation or a loss of control, regain Balnazzar before the group resumes full damage.
Healer- Preserve mana for the health-restoring transformation. Stand beyond Shadow Shock, remove Sleep when possible, and cover the new boss target if Mind Control takes the tank out of action.
Damage- Keep resources for the demon form. Crowd-control a mind-controlled ally instead of including that player in area damage, and keep the fight inside cleared space for Psychic Scream.