Activate Chthonian Nightmare by paying an amount of E, sacrificing a nontoken creature and returning Chthonian Nightmare from the battlefield to your hand.
When the creature dies, Pitiless Plunderer triggers, creating two Treasure tokens due to Mondrak.
Resolve the Chthonian Nightmare ability, returning another creature from your graveyard to the battlefield.
Activate two Treasures by tapping and sacrificing them, adding 1.
Cast Chthonian Nightmare by paying 1.
When Chthonian Nightmare enters, it triggers, causing you to get EEE.