I think I should make it more clear that the entire game was around ten turns, and he didn't get the scorpions out until about halfway through. And the big point is that the poison is dependent on you playing cards, which means that the only time it's useful without being OP is if the one infected only needs to play a few more cards, otherwise it's special poisoning ability is either useless, with all the cards already in play, or OP, where you still need to play a good number of cards. The point I want to make is that the poison should be dependent of the cards played.
Of course, thinking more about it, I guess the fact that it can be useless as much as OP is actually a good reason not to nerf it.