Vaermina, the Dreamweaver

Indestructible, Intimidate, Menace
Nightmares you control get +1/+1
At the beginning of each end step put a 0/1 black Nightmare creature token onto the battlefield for each player with ten or more cards in their graveyard.
Vaermina, the Dreamweaver enters the battlefield with X +1/+1 counters on it.
{u}{b}{t}Target player puts the top X cards of their library into their graveyard.