Xien, Hero of Massacre

Menace
Attacking creatures you control have +2/-1 until the end of turn. Transform Xien, Hero of Massacre at the beginning of your end step into an enchantment if you lost 3 or more life during your turn, and it has: Creatures you control have Menace and Xien, Hero of Massacre it's an enchantment as long as your life total it's above 10. It gains +X/+0 where X is 10 minus your total life.