I been wondering since i first start the game and i still havent get any answer of this.

What are the differences between each monster that we face?

Do they act like a witcher/zerker/pally in any way? resistance to some type of spell? Do they drop different type of armor?
Do they have speciality? IF yes, can u please share with me, what it is.. I am very interested to know. Please help.

Oh, please tell if u r sure bout it..not just guessing.

I notice some mob behave differently, some will go defense from start all the way.. but that is the only thing I know so far..