I think I have to play Hostage Chess to know exactly what you talk about. I recommend you to study all the zillions commands of add (add, add-copy, add-partial, add-copy-partial). Also, study the zillions files for Checkers and Hostage Chess. If it's too complicated to implement then take that as a sign to make the game simpler. If this is what you strongly believe in, then it worth the time. You'll love it when it works out right.