At the beginning of your precombat main phase, each opponent loses X life and you gain X life, where X is the number of Shrines you control.
If Sanctum of Stone Fangs leaves the battlefield while its ability is on the stack, you may control no Shrines as the ability resolves. In that case, no player gains or loses any life.
In a Two-Headed Giant game, Sanctum of Stone Fangs causes the opposing team to lose twice X life and you to gain X life.
Each Shrine has an ability that counts the number of Shrines you control. These abilities include the Shrine they’re printed on.
Shrines count only enchantments with the subtype Shrine. Other cards with “shrine” in their name (such as Jungle Shrine, Luxa River Shrine, and Nantuko Shrine) don’t count.