Ruins of Mylis Keep

{t}: Add {c}.
{1}, {t}: Add {b}. When this mana is spent to cast
your commander, it gains devour 1. (As it enters
the battlefield, you may sacrifice any number of
creatures. That creature enters the battlefield with that
many +1/+1 counters on it.)
Nobody knows what lurks within, for those who
venture through the gates do not return.