Shan-Kong, Indomitable

{x}{g}, {t}: Mill X cards. For each milled card with
mana value X, you may cast that spell from your
graveyard by paying {3} rather than paying its
mana cost.
At the beginning of your combat step, if you
have 40 or more cards in your graveyard, you
may create two 3/3 red and green Ballista artifact creature tokens with "{1}, {t}: Ballista deals 2
damage to any target."