Not sure what strategies you're comparing to in order to come to the conclusion that buffing Scorpions is OP. It certainly wouldn't dominate the meta in any way. It would make scorpion decks a bit more viable, but still not match up to most top decks.
All of these actually seem very useful. Since Crystal Scorp is immaterial, you'll easily start adding 2-3 Poison each turn fast even if you're -not- playing a lot of them, because if you're not, you're probably playing Phase Dragons. A lot better than Stalker.
The Fire, Water and Air ones definitely seem the strongest by virtue of incredible versatility. The former two are balanced by the fact that it's not a guaranteed effect and that creatures always get to attack before the effect takes place. The Air one is balanced due to low chance, but will synergize extremely well with Fog Shield. Playing that with Poisons and Arsenic off the mark would be a very strong deck (which I like).
