Brachiosaurus, Elder One

Reach, empower, vigilance
Whenever Brachiosaurus, Elder One deals
combat damage to an opponent, exile the top
card of each opponent's library. You may cast
any number of spells from among those cards
without paying their mana costs. For each card
you don't cast this way, put a number of +1/+1
counters on Brachiosaurus, Elder One equal to
that card's mana value.