Pony Fantasy VI Remake

Okay, getting into this again, for enemies. In terms of AI script I'm not doing much for existing monsters, just giving them better abilities. Most of my balance work is on increasing stats.

The biggest challenge for me is doing my custom boss. It's going to be fought in the Art Gallery, and initially appears as a Shadow that cannot be harmed - once a curative spell or item is cast on it, the boss changes into another form where it is vulnerable, and then fights for a bit before changing back. That all said, I'm planning to cobble together an AI script from Chadarnook (for the changing) and the Guardian (invincibility) The concern I have is that I see Hex is involved, and that worries me. Is there a tutorial for writing monster AI scripts somewhere?

Additionally, I looked and saw several tutorials with different ways of doing it - monsters with more than 65535 HP. What is the best way to do it?