From the Royal Arch trail, climb over Hammerhead, or from Sentinel Pass, hike west past Hammerhead. Hike roughly 100 yards uphill from here and look for a grungy formation in the woods.
Initially, this climb appears marginal... at best. The first few feet of the formation are heavily covered in lichen, moss and pine-needles. However, this formation is actually quite a bit longer than it initially appears, and the upper climbing is considerably better. I wouldn't go out of my way for this one, but it certainly provides a different route to Green Mountain Pinnacle or Challenger.
I found the best climbing on the right (north) side of the formation. The exposure here (to the north) is actually quite a bit greater than one would expect, as the ground drops off steeply below. The face here is full of several horizontal cracks, reminiscent of the fifth(?) pitch of the First.
Directly below the summit is a final headwall. Staying directly on the northern crest of the formation might become problematic at 5.0 here, so I traversed a few feet left. Roach suggests the headwall is simplest and only 4th class in the center. Climb west for 25 feet or so to the surprisingly small summit.
Note: Clearly, this face sees little activity as many holds are loose and still lichen covered. I personally broke a few flakes.
Descent: Scramble 20 feet southwest to hiking territory, negotiating a pretty gnarly looking fin. A dead tree is leaning up against the back of the formation, but I wouldn't trust it!