java -Xss4096k -jar proguard.jar
If you're still getting a Proguard exception, then there's something seriously wrong in the code. (Perhaps you ran it through an older obfuscator that puts in invalid links to confuse decompilers?)
No, no older obfuscators. I do have 3 classes, one main that extends JComponent and two very small helpers (~200B each) that I needed because I have to do some sorting and didn't want to be using Integer, what with all the casts, .intValue() calls, etc.
I do think I am doing something very wrong, though - I commented out all the AI code that I thought would be the bulkiest, and it only removed 2K from the final jar. This is my 3rd rewrite - I'm starting to think it's just not possible. But then again, it has to be - Riven got 3D cards working with gameplay in 4K - I'm only doing 2D cards!