Gresner, the Aggregate Engine

Gresner gets +X/+X where X is the total mana
value of all cards exiled by Gresner.
Exile a nontoken artifact you control: The next
artifact spell you cast this turn cost {w}{u}{b}
less to cast.
{4}{u}{u}: Shuffle all cards you own exiled by
Gresner into your library and draw that
many cards.