Amnennar the Coldbringer

Spiral of Thorns
Glutton patrols the bottom of the spiral. Clear a space for that fight, then follow the winding ramp to Amnennar at the summit. Look for the rare Ragglesnout during the climb and continue if he is absent. Follow the ramp instead of trying to cross the gap near its entrance, and finish each caster pack before the next patrol reaches it.

Amnennar the Coldbringer
Elite UndeadAmnennar tests control of the summit platform when Frost Nova roots players, Amnennar's Wrath knocks them back and summoned enemies reach the group.
Abilities

Frostbolt
Inflicts Frost damage to an enemy and reduces its movement speed for 4 seconds.
Interrupt Frostbolt to reduce Frost damage and avoid its movement slow when repositioning on the platform.

Frost Nova
Inflicts Frost damage to nearby enemies, immobilizing them for up to 8 seconds.
Keep the healer and ranged attackers outside Frost Nova's nearby blast. A rooted player cannot reposition normally for the next knockback or incoming enemies.

Amnennar's Wrath
Knocks an enemy back.
Tank with your back toward the tent or another solid backstop, not the platform edge, so Amnennar's Wrath cannot throw you down the spiral.

Summon Frost Spectres
Let the tank collect the summoned enemies on the platform. Stop any that reach the healer before returning damage to Amnennar rather than chasing them down the ramp.
Tank- Put a solid backstop behind you for Amnennar's Wrath and collect the summoned enemies without leaving the summit. Keep Amnennar within interrupt reach instead of chasing a summon toward the edge.
Healer- Stay outside Frost Nova's reach where possible while keeping the tank in range at the backstop. If a summon attacks you, bring it toward the tank on the platform rather than retreating down the spiral.
Damage- Interrupt Frostbolt and stop summoned enemies that reach the healer. Keep your own back away from the platform edge, and do not pull the group down the ramp while handling a summon.