Assassin Rouf is a foe in Digistruct peak Challenge DLC
Rouf is alone here and just as fast moving as he was before. The good news is he still has his shotgun. Keepign back and making good use of cover will make him fairly easy to beat.
Divide your attention between Rouf and the Taskmasters. It is important not to let Rouf distract you completely from the Nomads else they will easily overwhelm you.
If you are after the optional objective to take down Rouf with a Shotgun, move in close and loose your most powerful at him. If you are several levels above him, then things are a lot easier. Otherwise, there is a lot of weaving and ducking.
Fire and headshots.