The difference between this and something like [card]Titania's Chosen[/card] or [card]Elvish Vanguard[/card] is that this doesn't trigger off spells that you play. Titania's Chosen, in particular, was strong, because one could easily expect to put it in a green deck. Elvish Vanguard was weaker, because it only triggered off elves, but again, you could expect it to be played in an elf deck. This card doesn't benefit from the other cards in your deck. On the other hand, the type of spells on which it triggers is quite a bit lighter. If Elvish Vanguard popped up in a draft, he could be hard to play, since you definitely couldn't count on an opponent to play elves and you might not have many, yourself. This, on the other hand, is almost guaranteed to grow, whether you can help it along or not. I suppose that definitely
does merit being more costly than Elvish Vanguard. I'd be willing to knock it down to a 1/1 and make it cost

{G}. That would put it on par with Titania's Chosen, which is where I think it belongs.