Aura of Necro

Whenever a nontoken black creature goes to your graveyard, put an Aura counter on Aura of Necro.
Return Aura of Necro to its owner's hand: Add
an amount of black mana equal to the number of
Aura counters on this card. If this mana is used
to cast a spell without Necro, Aura of Necro
deals an amount of damage to you equal to that
spell's converted mana cost.
{b}{b}{b}, Discard Aura of Necro: Draw a card.