Gloomwake Putrimancers

Defender, Indestructible
If your devotion to black and blue totals less than 7, Gloomwake Putrimancers isn't a creature.
{x}{u}{b}: Target opponent loses X life; then, exiles a number of cards from the top of their library equal to 1/4 the total creatures on the battlefield rounded down.
{3}{u}{b}: Sacrifice a creature you control, each opponent loses 3 life.