Murderer of Crows

Murderer of Crows enter the battlefield with
four -1/-1 counters.
Flying, Menace
Contagion {b} (Whenever another creature enters
the battlefield, you may pay {b}. If you do, move a
-1/-1 counter from this creature onto it.)
Each creature with a -1/-1 counter on it loses
flying and cannot gain flying.