Jake Wrote:I'm pretty sure you can't copyright/patent gameplay, so I'm willing to bet your safe

You can't patent gameplay, but you can patent the algorithms behind the gameplay. Doom 3 suffered from this with its shadow-rendering I believe, since Creative owned the rights to this algorithm. ID and Creative made a compromise. ID could ignore the patent if they used Creative EAX.

Still, such patents are relatively rare and certainly nothing worth worrying about in an indy project. As a general rule, you can copy battle systems as you please.