Topologic Zeroboros

When Topologic Zeroboros enters the battlefield, place 1 +1/+0 counter on this card for each exiled card.
Whenever you cast a creature, exile all cards on the battlefield.
At the start of the Main Phase, if Topologic Zeroboros was exiled by it's own effect: Cast this card without paying it's Mana Cost, and if you do, it gains haste.