Re: Designing clone games
I'm not a lawyer or anything but in general, here's the idea: rules cannot be copyrighted. Only the particular expression/presentation of the rules can be. To be totally on the safe side, you'll want to write it from scratch, avoid any reference to Amazing Engine (even if it was just to point out it is compatible with it) but technically, you could keep the math intact and still totally be clear legally.
Many people prefer the safety of an open license to clone, such as the OGLed DnD, even though legally, you can do without. Since Amazing Engine was never opened, you'll have to do without this if you want to produce a clone.