Vreyu, Mage Of Doom

When Vreyu, Mage Of Doom enters the battlefield, you may tap target creature. If you do, exile Vreyu, Mage Of Doom. Whenever Vreyu, Mage Of Doom leaves the battlefield, you may destroy target tapped creature.
If you control no creatures, you may cast Vreyu, Mage Of Doom from anywhere as though it had flash.