Instructions
Toggle all of your pet's special abilities to manual control. You don't want to waste your ghoul's stun early on in the fight. Switch to "Unholy Presence." Cast "Horn of Winter" as you enter the fight. Cast "Death and Decay" on the ground in front of you as the Frost Mage approaches.
Avoid the Mage's "Frost Nova" if possible. Cast "Icy Touch" as the Mage comes into range. Cast "Plague Strike" if the Mage stays in range long enough for you to apply this disease as well.
Send your ghoul after the Mage and activate its "Stun" ability to force the Frost Mage to blink. Death Grip the Frost Mage over and use "Obliterate," "Scourge Strike" and "Death Strike."
Apply "Chains of Ice" to slow your Frost Mage opponent. Cast "Anti-Magic Shield" and use "Strangulate" and "Mind Freeze" to keep the Mage from casting spells. If you are taking a significant amount of damage, use "Lichborne" and target yourself with "Death Coil" for an extra heal. Cast "Icebound Fortitude" to reduce incoming damage as you finish the Frost Mage off.