Black Lives Matter

Whenever a creature you control with power 2 or less attacks, you may pay {B}. If you do, put a solidarity counter on target creature.
Creatures with solidarity counters on them have protection from spells and abilities your opponents control as long as Black Lives Matter is on the battlefield.
At the beginning of your upkeep, if you control three or more creatures with a solidarity counter, sacrifice Black Lives Matter; return it transformed under its owners control.