RTF is a global modification that replaces all towns in the game.

Water - I agree
Air - there's already a storm petrel
Earth - ents would be better

I don't know about ents, they're slow, so they'd need to have their initiative increased. As for the storm petrels, it seems like they introduced Simurghs and Simargls instead of the birds.

Added 2 minutes later
I was also thinking that we could work on the lizards and give them a call that summons some kind of ancient ancestor (an enhanced dragon lord, for example, not a fire one, but some kind of ice one, with immunity to water, possibly air or earth).