Mahra, Fear Incarnate

Mahra, Fear Incarnate's power and toughness
are equal to the greatest number of cards in a graveyard.
Nightmares and Horrors you control have
Menace.
Whenever a Nightmare enters the battlefield
under your control, each player discards a card.
Whenever a Horror enters the battlefield under
your control, each player mills a card and you
lose 1 life.