Riverguide Sanctuary

({t}: Add {u} to your mana pool)
As Riverguide Sanctuary enters the battlefield, you may reveal a Merfolk card from your hand. If you don't, Riverguide Sanctuary enters the battlefield tapped.
{t}, Pay 1 life: Add {g} or {w} to your mana pool
Where Merrow and Selkie meet, landstriders avoid.