To draw out the warchief you'll need to rack up some stealth kills. To hit one optional objective, you'll need to do so quickly. While there are two tempting targets just inside the gate, do NOT start your stealth run by waltzing in the front door. It's gauche. Also, the caragors will spot you.
Instead, climb the left tower, and continue working your way left around the outer perimeter, using aerial stealth kills and chained kills. Your first is just under the parapet.
Next, sneak just a bit forward to skrag one by the hay wain.
Return to the wall and continue your earlier heading. You'll see one marked guard on patrol up top, and two guards clumped together on the ground level, near the grog. Stealth kill the first and stealth chain kill the other two to meet your objective.
Tricky himself is a bit of pushover- use arrows and environmental attacks (flies and grog, mainly), to dispose of his clones.
He also has a fear of pinning- use it to keep him dazed while you take him apart with sword or bow. When he breaks, just remember to use Shadow Dominate (by far the most convenient method of Domination), and the mission's complete.