Cranious, The Skull Dragon

Whenever a creature your opponent controls is destroyed, place 5 skull counters on Cranious.
If cranious would be destroyed, sacrificed or
exiled you may pay {b}, remove 3 skull counter
instead.
During your draw step you may pay {g}, reveal
the top card of the library, if it is a permament
with converted mana cost less then the amount
of skull counters on Cranious, place that card
onto the battlefield, otherwise exile it.