Mikaeus, the Unhallowed, Soulstinger, and Ashnod's Altar

Prerequisites

• Mikaeus, the Unhallowed on the battlefield
• Soulstinger on the battlefield
• Ashnod's Altar on the battlefield
• Soulstinger does not have a +1/+1 counter on it

Steps

1. Activate Ashnod's Altar by sacrificing Soulstinger, adding
2. When Soulstinger dies, its second and undying abilities trigger
3. Resolve the first trigger, allowing you to put a number of -1/-1 counters on a creature equal to the number that were on Soulstinger
4. Resolve the undying trigger, returning it from your graveyard to the battlefield with a +1/+1 counter on it
5. When Soulstinger enters the battlefield, its first ability triggers, putting two -1/-1 counters on it
6. Repeat

Results

• Infinite -1/-1 counters
• Infinite colorless mana
• Infinite death triggers
• Infinite ETB
• Infinite LTB
• Infinite sacrifice triggers