What Lurks in Dreams

Whenever a creature becomes tapped, put a
nightmare counter on that creature. It doesn't
untap during its controller's untap step for as
long as it has a nightmare counter on it.
When there are no creatures without nightmare counters on the battlefield, sacrifice What Lurks
in Dreams and destroy all creatures. Each
opponent discards X cards and you draw X cards,
where X is the number of creatures destroyed
this way.