When Chthonian Nightmare enters the battlefield, you get
![Emblem e](/images/productsymbols/e_icon.gif)
![Emblem e](/images/productsymbols/e_icon.gif)
(three energy counters).
Pay X
![Emblem e](/images/productsymbols/e_icon.gif)
, Sacrifice a creature, Return Chthonian Nightmare to its owner's hand: Return target creature card with mana value X from your graveyard to the battlefield. Activate only as a sorcery.