Anti-Mage
Rare
8g/18r
Illusion
Attack:30+N
Discards all opponents Mage cards
N=Opponents hand total gem cost/3
I find the numbers quite high, though. The illusion keyword and the cost on a rare almost justify alone the 30 damage and the discard effect. The scaling damage can go to ridicilous numbers, give the hand of course. Lets look at some cards:
Magic well: 2 dmg
Meditation: 5 dmg
Red Mage: 4 dmg
curse: 16 dmg
Frost and Moonlight Unicorn: 10 dmg
Gateway: 20 dmg
The scaling this effect can cause can scale to devestating levels. So i belive that a dmg cap would be usefull. It would reduce the random spikes of the effect.
In any case, i would suggest an increasement of the cost.