There is an Achievement for "Goliath, Meet David – Allowed a Goliath to level up four times before killing him" but I don't know how Goliaths work to figure out how to do this.
When I've come across them before, they seem to attack me until I behead them, then some weird shrunken head atop of stringy neck comes out and they start rushing towards their friends (my enemies) and attack them until there's none left.
So how and why does this happens, and what are the actual Goliath AI rules? How do they "level up"?
Best Answer
When you knock off a Goliath's helmet and the little terrifying David Lynch head comes out, they go berserk and attack everyone. They level up by killing their former allies.
An easy way to tell whether or not you've gotten it to a high enough level for the "Goliath, Meet David" achievement is if the Goliath has God in its name.