The Philosopher's Stone is an item that allows your horse to become immortal, meaning it can live forever. It offers an advantage: if your horse is an immortal mare, she can reproduce as many times as she is covered during her entire life.
The stone is not passed down during breeding. It is solely for the horse it is applied to.
This item can now be earned from the tutorials that help you start your game, once you have registered.
This item costs 3 passes in the Black Market.