Mairsil, the Pretender, Endling, Cauldron of Souls, Blood Vassal, and Urabrask the Hidden

Prerequisites

• Mairsil, the Pretender on the battlefield
• Endling in exile
• Cauldron of Souls in exile
• Blood Vassal in exile
• Urabrask the Hidden on the battlefield

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 Endling's third ability by paying , giving Mairsil undying until end of turn
5. Activate Mairsil using Blood Vassal's ability by sacrificing it, adding
6. When Mairsil dies, its undying ability triggers, returning it from your graveyard to the battlefield with a +1/+1 counter on it
7. Repeat

Results

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