I think the argument can be made that Mana Reservoir is the better card. Which is to say, both might be bad. Mana Reservoir reads "give your spells +1 damage" while Frog reads "Give your spells +1 damage to a single random minion." I actually think the fact that it can't go face is a big deal. It's meta dependent, but it might just be better to have your Shooting Star deal 2 to all minions than to deal 1 to all +1. In a world where Mage has ping, is Dart Frog unnecessarily redudant? I don't know.
At the point where I'm playing either, maybe Celestial Emissary is the better card anyway.
How would you fix it?
I feel like a 1-mana, 1/3 is probably too good.
2-mana 2/3? Is that more reasonable?
I still stand by this.
Tempo mage rises again?