A remote plateau summit just west of Granite Peak, reached via the Storm Lakes basin above Mystic Lake.
From the West Rosebud (Mystic Lake) Trailhead, follow the standard approach along Mystic Lake to Princess Lake and into the Storm Lakes basin (the same general approach used for West Granite Peak). From a saddle above Lower Storm Lake at 10,720 feet, climb a narrow gully for 400 feet onto a broad scree/talus field, then continue about 600 feet to gain Mystic Mountain's north ridge at 11,700 feet. From there, walk south along the ridge for about a mile to the summit, staying to the east side of the ridge to avoid the harder sections directly on the crest. Round trip from a Princess Lake camp to the summit and back is reported at 8.3 miles.