Nerub'enkan

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.
Nerub'enkan
Elite UndeadNerub'enkan combines an armor penalty with webs and summons, making it dangerous to scatter away from the tank on the ziggurat approach.
Abilities

Encasing Webs
Immobilizes an enemy and increases the time between its attacks by 100% for 6 seconds.
Encasing Webs roots its victim and slows their attacks. Keep the fight in cleared space so the rooted player does not need to escape another pack.

Pierce Armor
Reduces an enemy's armor by 50% for 20 seconds.
Pierce Armor reduces the victim's armor; prepare tank mitigation and healing for the resulting melee pressure.

Crypt Scarabs
Summons 6 Crypt Scarabs to aid the caster in battle for 10 seconds.
Gather the summons beside Nerub'enkan and use cleave or area damage without moving the boss into uncleared streets.

Raise Undead Scarab
Protect the healer from this additional summon before returning to uninterrupted boss damage.
Tank- Keep Nerub'enkan and the summons together on the cleared ziggurat approach. Use mitigation when Pierce Armor is active instead of trying to solve the armor loss by retreating through more packs.
Healer- Expect the tank to need more healing during Pierce Armor. Keep rooted players in reach and bring a pursuing summon back toward the tank rather than running down an uncleared street.
Damage- Use cleave on summons once the tank has gathered them, then return to Nerub'enkan. Do not chase a stray attacker through another pack while Encasing Webs prevents the group from following.