"Fight" (see innistrad previews) is probably the creature removal that's most appropriate in green. (The example given has a cost, but it may or may not still make sense for as long as it's contingent somehow.)

This card may or may not work as is: it's supposed to be useful in a deck which turns opposing creatures into fungus, but it's obviously also REALLY useful against a fungus deck.

I also considered a spell with "two target funguses fight each other" with the dream of getting two opponent's creatures to fight, but that would normally be a 2-for-1 against a fungus deck. (I guess it could be costed at GGG so it can only be played in green decks.)

I'm not sure about the flavour. "Fight" is very green removal, but funguses fighting each other isn't quite "will of the hive". Edit: perhaps it should put a small token into play as replacement, then it could be a bit stronger but not as unblanaced and feel less unfungusy?

I like it. If Fun Guys (Naming the archetype right now!) gets to strong, it will balance it self in the mirror. I like it a lot. As for the flavor, I have absolutely no idea at all.

Oh, Innistrad...
Anyway, yeah. I don't know about this flavor. I do think the ability is probably the best green removal, but it does seem a bit weird in a fungus hive setting.

I love this card. We can make the flavor work.

Rourke: thanks. Perhaps something like, expelling the weak members of the tribe? Or putting a +1/+1 counter on the winner, to represent the strength being reabsorbed?

Memo to self: we have to decide if cards are going to key off "fungus or cards with +1/+1 on", or if cards that put +1/+1 counters on are going to say "it counts as a fungus", or if there's going to be static abilities making +1/+1 creatures count as funguses.

It may be too wordy, but I'd like all permanents that give +1/+1 counters to say that "Creatures with +1/+1 counters on them are Fungus".

"In addition to their other types" is probably too many words, so I'd scratch it... especially considering that removing other types is roughly what is happening, flavor-wise.

Green fighting: No problem with this being a green ability. I agree, the flavor is a bit off for fungus, though. The winner getting +1/+1 helps. "Target Fungus creature fights target non-Fungus creature" also works... though, I don't know how many of those you can print. Maybe a Sorcery, a rare with an activated ability and a Fungus that fights non-Fungus? 3? Did you really need more than that anyway?

This is starting to make me want an "Enchant Fungus", but if these creatures keep changing back and forth between Fungal states, I guess this would be a bad place to introduce the concept...

One of the things I like about it is that it fights fungi. I do like the "Creatures with +1/+1 counters on them are Fungus" idea.