Mikaeus, the Unhallowed, Shilgengar, Sire of Famine, and Heartmender

Prerequisites

• Mikaeus, the Unhallowed on the battlefield
• Shilgengar, Sire of Famine on the battlefield
• Heartmender on the battlefield

Steps

1. Activate Shilgengar by sacrificing Heartmender
2. When Heartmender dies, its persist ability triggers, returning it from your graveyard to the battlefield with a -1/-1 counter on it
3. Resolve the Shilgengar ability
4. Activate Shilgengar by sacrificing Heartmender
5. When Heartmender dies, its undying ability triggers, returning it from your graveyard to the battlefield with a +1/+1 counter on it
6. Resolve the Shilgengar ability
7. Repeat

Results

• Infinite Blood tokens
• Infinite ETB
• Infinite LTB
• Infinite death triggers
• Infinite sacrifice triggers