Cassiopeia, Serpent's Embrace

At the beginning of your upkeep, if a creature
has one or more -1/1 counters, put a -1/1
counter on that creature
{3}{g}{b}{b}: Target creature gets a -1/1 counter
{3}{b}{g}{g}: Creatures that didnt enter the battlefield this turn can't attack
Secrets are sharper than blades.