Amaira, Angel of solitude

Hexproof, Indestructible.
When Amaira, the Angel of solitude enters the battlefield no other creatures can be cast
When Amaira Angel of solitude is untapped it has hexproof and indestructible.
Amaira Angel of solitude's power and toughness is equal to the number of cards in your graveyard.
When your life total is above 20 this card is exiled