Fierce Flock

Flying
When Fierce Flock enters the battlefield, sacrifice all creatures you control that have flying. Fierce Flock gains {x} +1/+1 counters where {x} is the total strength of every creature sacrificed this way.
If Fierce Flock would be dealt damage, prevent that damage and remove 2 +1/+1 counters from it, then create a 1/1 white bird creature token with flying.