Perhaps. Darkness' theme is using your opponent's strength against them, and this is a good representation of that. While it does counter one growth creature per wolf, this is not always the case. Likewise, it is relativly weak, as its defense does not scale as with some growth creatures. On the other hand, I could (as you suggest) make it static and not dynamic. Though I wonder if that would require a wording change, as I'm lazy and don't want to have to redo the card image if I don't have to.