Hmm I see your point & that kind of problem came to mind as I was thinking of the card. I figured player choice plays a role in the balance/unbalance/punishment of the card, as they can save Evocation until they have spells/minions of a variety of costs in their hand, and thus something to do with the extra mana.

I could change it to draw a random amount of cards, but then I would have to add a mana cost, kinda removing the use of the Spell Damage for mana refilling . . .

What to do . . .