Caller of Dednap

When Caller of Dednap enters the battlefield, you may put Dednap, Void of the Grove from anywhere into your hand.
When you cast Dednap, Void of the Grove, you may sacrifice Caller of Dednap or exile Caller of Dednap from your graveyard. If you do, you may add X black or green mana to your mana pool where X is Caller of Dednap's converted mana cost. Only use the mana produced this way for casting Dednap, Void of the Grove.