Doomed to the Helvault

When Doomed to the Helvault enters the battlefield, exile target creature or planeswalker until Doomed to the Helvault leaves the battlefield. If the exiled card was a creature, you gain life equal to its toughness. If the exiled creature was a planeswalker, you gain life equl to the number of loyalty counters on it.
The Helvault claimed Nahiri, and she vanished into a darkness vast and total.