Crow's Cage

When Crow's Cage comes into play, attach it
to target creature. Target creature can't
attack or block. At the end of each turn, put
a -1/-1 on target creature. If target creature
attached to Crow's Cage would die, you may
pay {b}{b}. If you do, attach Crow's Cage to
another target creature. Otherwise, sacrifice Crow's Cage.