Interesting idea. Do the counters stack? E.g. if targeted by 2 of theses, would the creature grow by +2|+2 each round?
If so, then with many of these in play, you could quickly make something start growing VERY rapidly.
That could be a vicious combo if used with something that has a moderate amount of hp to begin with... The voodoo doll combo would be just wrong...
(a few of these + voodoo doll ... maybe throw in black nymph or liquid shadow for poison and vampire as well)
I like the idea on the face, taking a moderate starting damage in exchange for a long term payoff, but getting the mix right could be tricky...
Has anyone looked at the cost per growth rate, etc. ?