This card has a great design. Kill something early with a guarantee to have a card to kill something big later. I could see a control/midrange mage replacing 2 Frostbolts + 2 Fireballs with 2 Torches + 2 Polymorphs for maximum removal options.
I'm really happy to run a freeze mage deck. This card makes it much more powerfull. You don't need to waste a frostbolt on strong early game minions anymore and you get a decent amount of additional burn in your deck. 18 more damage in total, which is insane.
Seems pretty good at first glance but I don't think it's good enough to see a constructed play. You're essentially giving up tempo for future value and tempo. Tempo Mage's damage spell slot is already full. Freeze Mage, well, you don't want to increase your deck size because that decreses your chance of drawing Alex or Antonidas. Maybe in some slow control Mage deck?