Gift of Purity

When Gift of Purity enters the
battlefield, you may put a -1/-1 counter on
every creature you control.
Any creature under your control that dies with
at least one -1/-1 counter on, is then exiled from
the graveyard. It returns to the battlefield at
the next end step.
The blue crystal is pure, it is safe. -Narad,
Grand Vizier of Unkept Promises