Hi, I'm not a actual speedrunner of this game but I love what you guys do and I have a question that I don't seem to find a trustworthy answer so far. What difficulty really changes in this game? Enemy AI, HP, damage?

Even FAQs on GameFaqs don't explain it. The only piece of info I found was on Strategy Wiki website:

"Game level determines amount of enemy health, amount and quality of bonuses you will find, and their effectiveness. You can choose between Easy, Normal, Hard and Expert. To see the ending, beat the game on any difficulty, but easy."

If that's true (more HP), shouldn't be separated rankings for Expert/Easy?

Thanks for reading