Aros, the Mistblade

Whenever you cast a spell, counter that spell
unless you pay {2}. If that spell is countered this
way, put it on the bottom of your library instead
of your graveyard.
Whenever you place a card on the bottom of your library, put a +1/+1 counter on Aros. Until the
end of your turn, the next spell you cast cost {x} less, where X is Aros's power and cannot be countered.