Wow that would by very nice from you. I have trouble mainly with the check/pate/mate because of there are many possible ways to ... you know stuff around it. It is hard to write what I mean but I think you get it

In order to check the check, you just need to see if the pieces of the opposite team can resemble the king's cage. To check the checkmate, you need to check the check + check the neighboring cells ( if they have a shape, you do not need to check them. With a check on the cover of figures and other things will be more difficult, you can just do this, if a person(when his king is under the Mat) does not go for 20-30 seconds, so he loses + it is necessary to do so that the king could not be killed, but already, I think, quite simple.

I think I get what you mean but making a program is a problem for me, algoritmic problem as I read yours is not a problem. But I am new to Greenfoot and I would like to wait to the moment when I go to college because now I am only on High School. Thanks for solution I will use it when the time will come :) And I have also one question. (beside chess) When I publish a scenario, it won't upload (just show initializing). I don't know what to do...do you know how to fix it?

About the download - sometimes the download is quite long(up to 5 minutes or more). About Greenfoot - you can study it yourself(in the help tab there is A greenfoot Library tab - there are all the commands and their description, perhaps I will download your game and make some kind of algorithm that should help you.