How do I launch an application with a specific JDK?
There's a support article from that game's developer addressing an issue where "the game freezes at start-up (blank screen)". It involves installing Java 1.6 (as you've done) and manually updating a library file, libjogl_awt.jnilib. However that article says the issue occurs when "[upgrading] to High Sierra", so this might not be what's causing your issue if you're still running Sierra.