Cave of Illusions

Cave of Illusions has hexproof and enters the the battlefield tapped
{t}: Add {u} to your mana pool. Use this mana only to cast illusion creature spells and activate abilities of illusion creatures.
{t}; tap three blue creatures you control: Illusion creatures you control get +3/+3 and gain flying and hexproof until end of turn. You may only activate this ability once each turn and only as a sorcery.