This show was a late 80s/early 90s Nickelodeon or Nick Jr. special, utlizing puppets and live action cast members. It definitely wasn’t The Dark Crystal. As I remember it, the basic premise was as follows:
Two factions of Goblins are trying to choose a king, and to do so they have to get a special crown before the end of one particular day. This day is the only time in which the crown can be touched, as Goblins can usually only move at night; if they are exposed to sunlight on any other day, they will turn to stone. The current king and his son are trying to claim the crown before the leader of the evil faction and his son find it. Somehow, a human boy became involved. At the end, the evil father and son are turned to stone.