Intense Cold

Intense Cold is a Lich King heroic achievement needed for the Glory of the Hero achievement, rewarding the Reins of the Red Proto-Drake. Keristrasza is the final boss in the Nexus.

Strategy
Movement breaks Intense Cold, so just keep strafing/jumping/moving, and avoid spells with long cast times. If you get rooted by Crystal Chains, use Free Action Potion or PvP trinket or whichever class/racial abilities you have to get out of movement-impairing effects. If you have a priest in the group, have all group members stand close to each other and use Mass Dispel.