XI has kind of a combination of scripted and AI. Some mobs will use x move always at y HP but a lot of the time, at y HP it just adds that move to their arsenal. For example, Cerberus won't use Gates of Hades(it's big move) until it's HP is equal or lower than 25%. It can use it anytime after it's HP is ~25%.

I can't help but feel like this is another example of the genre going backwards though. Although it seems like every genre is nowadays as publishers want every game to sell like Call of Duty. /shrug