Vaan, the Essence Mage

Whenever one or more cards enter your graveyard
from your hand or library, put a +1/+1 counter
on Vaan, the Essence Mage.
Whenever you would cast an Artifact, you may
remove any number of +1/+1 counters from
Vaan. If you do, that Artifact costs you {x} less,
where X equals the number of +1/+1 counters
removed.