Anti-momentum card? Like you said, seems awfully situational.
-1/0 for big creatures is not that great, seems like it only applies once, right?
Dragonhuman's post gave me an interesting idea for a card that would be something like "decay/rotting flesh" that causes creatures to lose -1/0 for each successful attack. You could add a clause like creatures with over 5 attack, but it's an interesting idea.