Sloth's Slumbering Isle

Sloth's Slumbering Isle enters the battlefield tapped with 5 sleep counters on it. It doesn't untap during your untap step if it has a sleep counter on it.
At the beginning of your upkeep, remove a sleep counter from Sloth's Slumbering Isle.
{t}: Add {4}{g}{g}{w}{w} or one mana of any color. If you use this mana to cast a spell, return Sloth's Slumbering Isle to its owner's hand.