Twins of Discord
From Modern Horizons 3 Commander set
Twins of Discord
Creature — Eldrazi
8/6
Whenever you attack, choose odd or even. Creatures with mana value of that quality can't block this turn. (Zero is even.)
Each other colorless creature you control has bloodthirst 2. (If an opponent was dealt damage this turn, that creature enters with two additional +1/+1 counters on it.)