Your Pharaoh has become the falcon-headed, lightning-wielding Son of Osiris. This unit has all the powers of a normal Pharaoh, such as countering Myth Units, and healing and empowering, but is much more powerful in combat. He is under your control and lasts until killed. He cannot be healed. If he is killed, you will regain a normal Pharaoh. 

Guard the Son of Osiris carefully; he will almost certainly become your enemy's favorite target.