Deciduous Shrine

As Deciduous Shrine enters the battlefield, you may pay 2 life. If you don't, Deciduous Shrine enters the battlefield tapped.

{t}: Add {g} to your mana pool.

{t}, Pay 2 Life: Exert Deciduous Shrine: Add {g}{g}
to your mana pool. (An exerted permanent won't untap on your next untap step.)