I think you should change the card name to "Curse".
well i agree with this, my first option was curse in fact, but i didn't really undersand why it's "blessing" insead of "bless", so i opted for this name
a cheaper version that does not do HP damage, but just weaken the attack.
it would be an option, however i choses this one because i think it yould be fun to weaken creature's both in hp & atk
like golden dragon or firefly queen (because with this card it would be more simple even to take them down)
however even your idea is interesting ^^