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He spawns from one side of the clearing, then runs up to the top of the small hill in the center.
When any of these fellwoods spawn, they are by themselves, but they wander until they have a tight group of 3 fellwoods. As they wander, they seem to re-sort, so that each group is all the same color. Best to kill them all, then pick them off as they spawn. They will agro one after the other, until they are all dead again.