It would be an online game where you are given the tools to create your own sidekick. You'd equip it with different parts, dictating it's speed, reaction time, firepower, weaknesses, and other attributes. You'd then take your creation on adventures/battles with other gamers.
You're sidekick's parts and allegience would be determined by which version of the game you bought (one for Magic, Science, Nature). Each race would exist on their own continent and have a reason to dispute one of the other two species.
In the beginning, your creation would only be the size of a dog. As you gain experience, your beast/robot/mutant could be as big as a skyscraper (and you could ride in or on it). All three games would interconnect. You can fight with other players online or ally to take on the common enemy that wishes to destroy all three nations.
Creating, competing, and communicating would be the hook that sucks you in. Character creation would be very user friendly, too.
