This mission is available after finishing the main story of the Mr Torgue DLC. It’s recommended that you only try to tackle him with a full party of players in co-operative play.
Distance is important. Try and stay as far away from Pete as possible at all times and deal the damage. If everyone brings Slag weapons then this fight wil go much, much quicker.
If you are hit by Pete’s nova attacks then you can use the valves around the arena to remove the de-buff, but doing so will increase the power of the fight’s additional mob,s so try and clean them up and leave the wash until the last minute.
This fight is simply long, so make sure you have healers and ammo dealers in tow.