Rhahk'Zor

The Deadmines
Follow the main mine passage to Rhahk'Zor and the guarded door. Clear his ranged escorts before finishing him, then continue through the doorway toward the side mine and lumber room.
Rhahk'Zor
Rhahk'Zor's Slam stuns the tank while his ranged Watchmen continue firing.
Abilities

Rhahk'Zor Slam
Keep the tank healthy before the Slam; its damage and stun arrive together.
Tank- Pick up Rhahk'Zor and his Watchmen in the cleared mine passage. Plan mitigation before the Slam stuns you rather than relying on an action during the stun.
Healer- Keep the tank topped up for Rhahk'Zor Slam, especially while the Watchmen are still shooting. The stun prevents the tank from reacting to its damage.
Damage- Kill the Watchmen accompanying Rhahk'Zor first so their shots do not overlap the tank's Slam stun. Finish Rhahk'Zor before moving through the guarded doorway.