Mikaeus, the Unhallowed, Heartmender, and Bloodflow Connoisseur

Prerequisites

• Mikaeus, the Unhallowed on the battlefield
• Heartmender on the battlefield
• Bloodflow Connoisseur on the battlefield

Steps

1. Activate Bloodflow Connoisseur 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 Bloodflow Connoisseur ability
4. Activate Bloodflow Connoisseur 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 Bloodflow Connoisseur ability
7. Repeat

Results

• Infinite +1/+1 counters on a creature
• Infinite ETB
• Infinite LTB
• Infinite death triggers
• Infinite sacrifice triggers