It's set sometime in around the, 1920s or something like that, but obviously its not like we knew it. This guy named Rex goes to find his dad who he hasn't talked to in years, and from there the story progresses (in campaign mode, that is). You are able to combine two animals; in campaign mode you first have to get their DNA before they are available to you, but in other modes you can use any of the, like 50 animals. For instance, you can combine a bat and a great white shark to get a flying shark...and what's more is that you can choose which parts of the animals you use; if you are using a cheetah and a giraffe for an example, you could use all four legs of the cheetah, or the front two legs of giraffe and the hind two of the cheetah; choose the head, the tail, and the body type, and with just two animals you can make quite an assortment! And every animal has special things about it, like the giraffe can see very far, the gorilla can pummel, the coyote and hammerhead can detect hidden units...lots of choices. Using theses attributes, you make your custom Impossible Creatures army, to beat the foes that stand in the way of you finding out what happened to Rex's father. Or, play with a friend with the online multiplayer mode.
If you like Warcraft/Starcraft, this is the game for you, because its the same concept in a way, but taken to a whole new level!