Ok so I've been trying out some different things on Legaia in an attempt to find a way to skip Xain as a boss. The only reason I feel like he would be the one boss that is skippable is that there is a glitch in the game that once Xain is beaten if you leave Octam through the shadow gate (just one screen out is fine) and door of light yourself back into Octam Underground all of the townspeople revert to thinking that Xain hasnt been beaten yet.
However the elevator back to the surface is still usable even though the guards dialogue still says you dont have permission, and Xain is still in fact dead. But its still one of the few programming errors I've found so I am optimistic there might actually be something there.
Now my issue is this; this is my first time doing anysort of Tool Assisted testing using RAM values and such, and for the life of me I cannot lock down what value changes between when you leave Octam and Door of Light back in to make it so the villagers revert their dialogue. If anyone else has a little bit more familiarity with Legaia and RAM values and would be willing to help out try and track this value down that would be a huge help