Magistrate Barthilas

The Gauntlet
Enter from the service entrance or return from the Scarlet branch, then work through Anastari's, Nerub'enkan's and Maleki's ziggurats. After each boss, enter its building and clear the Thuzadin Acolytes; leaving them alive keeps the route to Slaughter Square shut. Deal with Magistrate Barthilas before the square if the service-entrance approach sent the magistrate running. Black Guard Swordsmith is a plans detour by Anastari's ziggurat, and Stonespine is an optional patrol encounter rather than a gate requirement.

Magistrate Barthilas
Elite UndeadBarthilas combines growing Furious Anger with a knockback and nearby spell interruption, so positioning must preserve the tank's contact without exposing the healer.
Abilities

Furious Anger
Furious Anger builds the magistrate's attack pressure. Use damage cooldowns early and retain tank mitigation for the later part of the fight.

Draining Blow
Drains 250 health from an enemy, transferring it to the caster.
Draining Blow restores health to Barthilas while damaging the victim; keep the group focused through that recovery.

Crowd Pummel
Pummels nearby enemies for normal damage plus 10 and interrupts any spell being cast 75% of the time for 5 seconds.
Crowd Pummel interrupts nearby casters. Put the healing position outside the melee group.

Mighty Blow
Use a wall behind the tank for Mighty Blow. If Barthilas turns after a knockback, pause damage and bring the boss back toward the tank.
Tank- Use solid scenery behind you for Mighty Blow, with the healer outside Crowd Pummel reach. Keep a defensive for the growing Furious Anger pressure rather than using every cooldown on the opening hit.
Healer- Stay out of the melee group's Crowd Pummel and prepare for stronger attacks as Furious Anger builds. Keep the tank in sight after Mighty Blow instead of following the knockback into an uncleared pull.
Damage- Use offensive cooldowns before Furious Anger accumulates. If Mighty Blow sends the tank away and Barthilas turns toward you, move toward the tank and pause attacks rather than running deeper into the square.