Zyx, Ancient Undead

Hexproof
When you cast Zyx, Ancient Undead each player mills 4 cards.
When Zyx, Ancient Undead enters the battlefield exile all cards from all graveyards.
You may cast cards any player owns in exile as though they had flash. As long as you control Zyx, Ancient Undead.
You may spend mana of any color to cast spells from exile.