The Bratt Bullymong is the first true Bullymong you will encounter. It is capable of the full range of attacks such as leaps and throws that the smaller Monglets are not capable of. They are much tougher than the Monglets and can take 2-3x more damage. Because of their increased size, they are also faster and more agile.
The Brat Bullymong is replaced by the Savage Brat Bullymong in True Vault Hunter Mode.