Chthonian Nightmare and Priest of Urabrask on the battlefield.
You have at least three energy counters.
Steps
Activate Chthonian Nightmare by paying ({E} magic symbol) ({E} magic symbol) ({E} magic symbol) , sacrificing Priest of Urabrask and returning Chthonian Nightmare from the battlefield to your hand, returning Priest of Gix from your graveyard to the battlefield.
When Priest of Gix enters the battlefield, it triggers, adding ({B} magic symbol) ({B} magic symbol) ({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) ({E} magic symbol) ({E} magic symbol) , sacrificing Priest of Gix and returning Chthonian Nightmare from the battlefield to your hand, returning Priest of Urabrask from your graveyard to the battlefield.
When Priest of Urabrask enters the battlefield, it triggers, adding ({R} magic symbol) ({R} magic symbol) ({R} magic symbol) .