When Chthonian Nightmare enters the battlefield, it triggers, causing you to get ({E} magic symbol) ({E} magic symbol) ({E} magic symbol) .
Activate Chthonian Nightmare by paying ({E} magic symbol) ({E} magic symbol) ({E} magic symbol) ({E} magic symbol) ({E} magic symbol) , sacrificing a creature with mana value 1 or less and returning Chthonian Nightmare from the battlefield to your hand, returning Possessed Skaab from your graveyard to the battlefield.
When Possessed Skaab enters the battlefield, it triggers, returning Songs of the Damned from your graveyard to your hand.
When Chthonian Nightmare enters the battlefield, it triggers, causing you to get ({E} magic symbol) ({E} magic symbol) ({E} magic symbol) .
Activate Chthonian Nightmare by paying an amount of ({E} magic symbol) , sacrificing Possessed Skaab and returning Chthonian Nightmare from the battlefield to your hand, returning a creature from your graveyard to the battlefield.