Greedy Freebooter and Cloud Key on the battlefield (Cloud Key with "Enchantment" chosen).
({B} magic symbol) available.
Steps
Cast Chthonian Nightmare by paying ({B} magic symbol) .
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) , sacrificing Greedy Freebooter and returning Chthonian Nightmare from the battlefield to your hand.
When Greedy Freebooter dies, it triggers, causing you to scry 1 and create a Treasure token.
Resolve the Chthonian Nightmare ability, returning Shambling Ghast from your graveyard to the battlefield.
Activate the Treasure by tapping and sacrificing it, adding ({B} magic symbol) .
Cast Chthonian Nightmare by paying ({B} magic symbol) .
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) , sacrificing Shambling Ghast and returning Chthonian Nightmare from the battlefield to your hand.
When Shambling Ghast dies, it triggers, creating a Treasure token.
Resolve the Chthonian Nightmare ability, returning Greedy Freebooter from your graveyard to the battlefield.
Activate the Treasure by tapping and sacrificing it, adding ({B} magic symbol) .