Pass by the dead tree and scramble up the easy gully passing a live tree. Not much further and the terrain steepens and pro becomes desirable; this is probably a good point to set the belay. Tackle the steeper terrain while watching out for loose/crumbling rock. Surmount a ledge on the climber's right of the summit rock; this ledge is visible from ground level. A large loop of cord or webbing may be useful for pro. Finally climb left onto the summit rock and then run it out up to the anchors of Nightstalker.
Bob Kerry's Backcountry Rockclimbing in Southern Arizona has a description of Nightstalker that mentions "an old route up the east side [of Owl Rock] which is more of a mountaineering affair." This may or may not be that route.
From the start of Nightstalker and as viewed when looking down from above, hike roughly counterclockwise around the large boulder and the formation until reaching an easy gully. The entrance of the easy gully currently holds a medium-sized dead tree.
Take about half of a standard rack and also some care to avoid questionable rock. In other words, it may feel a little runout for the grade.