Monsters have an AI that depends on their how smart they are. (monster's Int) This applies only to NPC beasties, so ignore this for your characters.
IQ: 1-80. A stupid monster. Will randomly attack targets.
IQ: 81-120: Slighty smarter monster. This monster will automatically attack whoever is doing the most damage, and will attack healers if they're healing a lot. This is the most common type.
IQ: 121-140: Even better. Monster has the 'Detect Cast' ability that could stop spell/ability casting, and they know how to better take out your party depending on your class.
Int: 141+: Super smart. Will exploit your character's main weakness, and is every bit as organized and intelligent as you are. Usually has abilities that really make life very difficult for your party.
Monsters also have abilities like Super Strength, Tough Skin, etc. that can make fighting them a challenge. So even if they're not too bright, they could still take out your party with raw power. Monsters will gradually gain more abilities as you get stronger. You won't be fighting 'uber' baddies until much later in the game.
