Bullymongs are ape-like creatures that have four arms and are one of the first enemies encountered in the game. While some variations perform different attacks, most of them will move around and try to get within melee range to strike you with their meaty arms. Some kinds of Bullymongs will toss rocks at you, though, with one in particular (the Bullymong Slinger) running away from you if you get too close. Most Bullymongs will be found in cold climates, as well as in Eridium Blight, with those ones being called Bedrock Bullymongs.
The baby of the species and very easy to kill. All they do is charge at you and try to melee.
Similar to the Monglet, but with more health. They do the same thing, as far as attacks go.
The Bullymong Slinger will hang back and throw rocks at you. In fact, if you get close enough, they will back away from you so they can continue tossing rocks.
This version is a combination of the other Bullymongs, meaning they can come up to melee you, as well as toss rocks at you from a distance. They can quickly close the gap by leaping into the air and either landing close to you, or even on top of you. It prefers to perform the melee/jumping attack over throwing rocks.