Weirdly enough (although obviously it doesn’t actually mean anything) I was designing a card for just this thing in a dream recently. I just don’t remember what it did. I do have a design of this on our Guild forums. Funnily enough, it was also a 12/12 with a casting cost of 2UG, but that’s pretty much the extent of the similarities. Well, that and it couldn’t attack early either. Mine required you control 20 lands. It also had a partner and it gained a +1/+1 counter any time any player revealed a land card from their library or put a land card into play from the library.
Another green topic? Yes. Although, actually they were red at first.
The hydra of greek mythology was about growth. When it lost a head, two more sprung up. While that was exactly what the early versions went for, this proved quite difficult from design point of view, so they are more about +1/+1 counters and often scaling up when the game goes long.
Each color has its distinctive features and one of the features for green is its ability to ramp. Sure, all colors can produce extra mana in some way or another, but green is definitely the master of this, having several ways of doing it in most sets.
However, since I don’t want to go through all the ways green can do this (mana elves, doubling effects), I’m limiting this to noncreature cards that put lands into play from your library and are green (there are some white and colorless ones that do this as well). I’ll probably do a separate one on creatures at some point. I’ll also omit all the spells, that don’t actually add lands, but rather change the ones you already have into different ones, like Scapeshift which could be used to produce more mana in many ways, but generally isn’t.