Principal Guardian

Principal guradians are bigger than others guarians, but smaller than a badass. They have very high shields, and suprisingly high health for a gurdian. Ranged attacks are the best on them, exspecially with Mordecai, if you can just shoot through their shileds.

Principal Guardians are not only in playthrough one.

The first time you will see a Principal Gurdian if you are going through the game liniarly, is in a cave in the Dahl Headland.