Nurthest, Dragon of Dimir

When Nurthest, Dragon of Dimir enters the battlefield, return up to X creatures from your graveyard, you lose life equal to the converted
mana cost of each creature you returned this way.
{4}{u}{b}: Exile target creature from your
graveyard, deal X damage to target creature
where X is it's converted mana cost.
{1}{u}{b}: Draw a card.