Mairsil, the Pretender, Carnifex Demon, Cauldron of Souls, Blood Vassal, and Fervor

Prerequisites

• Mairsil, the Pretender on the battlefield
• Carnifex Demon in exile
• Cauldron of Souls in exile
• Blood Vassal in exile
• Fervor on the battlefield
• Mairsil does not have a -1/-1 counter on it

Steps

1. Activate Mairsil using Cauldron of Souls' ability by tapping it, giving itself persist until end of turn
2. Activate Mairsil using Blood Vassal's ability by sacrificing it, adding
3. When Mairsil dies, its persist ability triggers, returning it from your graveyard to the battlefield with a -1/-1 counter on it
4. Activate Mairsil using Carnifex Demon's ability by paying and removing a -1/-1 counter from it, putting a -1/-1 counter on each other creature
5. Repeat

Results

• Infinite black mana
• Infinite death triggers
• Infinite ETB
• Infinite LTB
• Infinite sacrifice triggers