Dark Immortality

When Dark Immortality enters the
battlefield put an immortality counter on target creature you control. That counter remains on
the creature as it moves to any zone other than a
player's hand or library and that creature is
Legendary as long as it has that counter.
When a creature with an immortality counter
would move to your hand or library exile it.
You may cast creature spells with immortality counters from your graveyard or exile.