Activate Ashnod's Altar by sacrificing Haunt of the Dead Marshes, adding CC.
When Haunt of the Dead Marshes dies, Pitiless Plunderer triggers, creating a Treasure token.
Activate the Treasure by tapping and sacrificing it, adding .
Activate Haunt of the Dead Marshes by paying 2, returning it from your graveyard to the battlefield.
Repeat.
This delightful loop relies on Ashnod's Altar to continuously sacrifice Haunt of the Dead Marshes, converting each trip to the graveyard into a pair of colorless mana. Because Pitiless Plunderer watches your creatures perish, every sacrifice also generates a Treasure token to help fund the resurrection costs. Finally, Haunt of the Dead Marshes provides its own built-in recurrence ability—allowing you to pay that mana and loop right back onto the battlefield, churning through your deck with infinite scry triggers along the way.