Ever play Zoo Tycoon, back in the day? You decide which animal you want, make an exhibit to suit them, place 'em inside and watch them frolic. Or maybe you're more interested in the visitors: You set up a nice path for them to walk, some benches for when they're tired, pleasant scenery to lift their mood, and plenty of food, drinks, treats, and souvenirs.
Minecraft has a small assortment of farm animals. Mo' Creatures has a good assortment of creatures both natural and unnatural. We're sticking to the natural (mostly - there's plans for at least a Unicorn), and putting together a huge list of animals, many of which we've already modeled and textured, and some of which we've already coded. We'll be developing AI's for Predators, Prey, and probably a couple other groups, so that if you release a gazelle near a lion you won't have the two politely ignore each other.
(Note: Sea animals and dinosaurs were expansion pack material in the original game. We're taking a similar tactic, and not messing with sea exhibits or dinos for the moment. If we eventually complete this mod, we'll consider creating a good expansion for those of you who are after bigger - or stranger - game.)
(Second Note: We will, however, be adding animals from the special exhibit houses in Zoo Tycoon - e.g., reptiles from the Reptile House and birds from the Aviary.)
Once you've tagged an animal (using a special tag gun), you'll be able to buy that type of animal for your zoo from a vendor GUI. So if you want a Panda, you go out and find a panda in the wild, tag it, and then come buy a new one for your zoo. (We might provide a "cheat code" to get past this requirement.) Animals inside your zoo will have hunger bars and happiness bars, and you'll need to be careful that these don't get too low.