You have a creature card with mana value 3 or less in your graveyard.
Steps
1Activate Chthonian Nightmare by paying at most , sacrificing Patron of the Arts and returning Chthonian Nightmare from the battlefield to your hand.
2When Patron of the Arts dies, it triggers, creating a Treasure token.
3Resolve the Chthonian Nightmare ability, returning another creature card from your graveyard to the battlefield.
4Activate the Treasure by tapping and sacrificing it, adding .
5Cast Chthonian Nightmare by paying .
6When Chthonian Nightmare enters the battlefield, it triggers, causing you to get .
7Activate Chthonian Nightmare by paying , sacrificing another creature and returning Chthonian Nightmare from the battlefield to your hand, returning Patron of the Arts from your graveyard to the battlefield.
8When Patron of the Arts enters the battlefield, it triggers, creating a Treasure token.
9Activate the Treasure by tapping and sacrificing it, adding .
10Cast Chthonian Nightmare by paying .
11When Chthonian Nightmare enters the battlefield, it triggers, causing you to get .