Aboleth, Nightmare Mother

Hexproof, skulk

Creatures your opponents control have -1/-1.

Whenever Aboleth, Nightmare Mother attacks, the
defending player mills 3 cards. Exile up to one
creature card from their graveyard. Create a copy of
that creature that's tapped and attacking, except it's
a black Nightmare creature instead of its usual types
and colors. Sacrifice it at the end of combat.