Rampart Shrine

At the beginning of your upkeep, you may
add {g}{g}{g} and, until end of turn, you don't
lose this mana as steps and phases end. If
you do, lands you control can't be tapped
for mana this turn.
{4}{g}{g}: Until end of turn, Rampart Shrine
becomes a 7/7 green Elemental creature
with trample.