Again, this may be too much with the Fungus theme, but I'd rather go too far in one direction then cut back, than do the other.

Originally, this gave +1/+1 for each Fungus in play. That was appropriate when Green was gung-ho for fungus, but now, the color is a bit mixed. That being said, I don't know why I didn't think of throwing an instant that gave +1/+1 counters in the mix in the first place. This is a straight upgrade to Battlegrowth, but I don't think anyone will complain. Battlegrowth was often last picked in Mirrodin.

Alternatively, this could give more counters to a creature for a higher cc, or it could be a lot more like Thrive. Also, also, this could give a +1/+1 counter, make all creatures with +1/+1 counters funguses until end of turn, then give a creature +X/+X where X = fungi... but I suppose that's getting too far into the realm of uncommon + is a bad idea.

I like how this is very simple, a minor upgrade on Battlegrowth which was quite a bad card, a decent common combat trick, and interacts with the set themes.