Thorin King Under the Mountain

When Thorin, King Under the Mountain enters
the battlefield, look in your library for a card
named Erebor and put in your hand.
{r}, {t}: Thorin deals damage equal to the amount
of Dwarves that entered the battlefield under
your control this turn to any target. Then, if
you control five or more Dwarves, put a +1/+1
counter on Thorin, King Under the Mountain.