Ashiok, Fear Unbound

Fear, siphon (This creature deals damage to
creatures in the form of -1/-1 counters and to players
in the form of milling cards equal to the amount of
damage dealt by this creature.)
Whenever a creature card is put into an
opponent's graveyard from their library,
exile that card and create a 2/3 blue and
black Nightmare creature token with siphon.