Credit goes to acaacovic for the freeze mage deck. (i've only made a couple of mods)

This deck works for BOTH heroic end bosses, though it can take a while to get the right card order.

you're delaying for the alexstrasa , then burn follow up.

This also works for Dragonlord Skruk, especially if you add a "mana bind"  that will catch his 15 damage to face spell for your use... I got it from magic trick spell

Then all you need do is delay till you play alexstrasa and use his own damage spell on him.