In the Civ IV mod Fall from Heaven II, there are a number of "Uniques Features" on the map. One of them is called the Ring of Carcer, a magic ring holding an angel called Brigit. The tooltip only says that a level 15 unit can enter the ring, but nothing about what happens when a unit enters. Is Brigit freed? Does she join the player or act as a barbarian? Something completly different?
Brigit joins your team. She is a hero with 6 attack, +3 holy, and +2 fire affinity. She has a movement speed of one and starts with the angel, hero, and immortal promotions.