Moss Covered Hollow

Hideaway 6.
Ward {2}.
Moss Covered Hollow enters the battlefield tapped.
{t}: Add {b} or {g}.
{b/g}{b/g}, {t}: You may play the exiled card without paying its mana cost if the combined total power of creatures you control plus the number of cards put into a single graveyard this turn is 10 or more.