Behemoth Transporter

Vigilance, trample, indestructible
Behemoth Transporter costs X less to cast for
each permanent you control with stock.
If Behemoth Transporter enters the battlefield
from exile, draw 10 cards, then exile it.
{t}: Exile Behemoth Transporter until the
beginning of your next upkeep, then return it to
the battlefield under its owner's control.