Activate Cauldron Familiar by sacrificing a Food, returning it from your graveyard to the battlefield.
When Cauldron Familiar enters, it and Cloudstone Curio trigger.
Resolve the Cauldron Familiar trigger, causing each opponent to lose 1 life and you to gain 1 life.
Resolve the Cloudstone Curio trigger, returning City Pigeon from the battlefield to your hand.
City Pigeon triggers, creating a Food token.
Activate Phyrexian Altar by sacrificing Cauldron Familiar, adding .
Cast City Pigeon by paying .
When City Pigeon enters, Cloudstone Curio triggers. Choose not to return anything to your hand.
Repeat.
This clever loop uses Phyrexian Altar as a mana-generating sacrifice outlet to fuel the cast of City Pigeon, which triggers Cloudstone Curio to bounce your creatures without needing to replay them manually every time. As City Pigeon enters and leaves the battlefield, its delayed departure creates the Food tokens needed to immediately revive Cauldron Familiar from your graveyard. The Familiar's entrance triggers both the Curio to safely retrieve your Pigeon and its own drain effect, letting you endlessly repeat the cycle to drain your opponents out of the game while generating boundless resources.