Mikaeus, the Unhallowed, Ashnod's Altar, and Kithkin Spellduster

Prerequisites

• Mikaeus, the Unhallowed on the battlefield
• Ashnod's Altar on the battlefield
• Kithkin Spellduster on the battlefield

Steps

1. Activate Ashnod's Altar by sacrificing Kithkin Spellduster
2. When Kithkin Spellduster dies, its persist ability triggers, returning it from your graveyard to the battlefield with a -1/-1 counter on it
3. Activate Ashnod's Altar by sacrificing Kithkin Spellduster
4. When Kithkin Spellduster dies, its undying ability triggers, returning it from your graveyard to the battlefield with a +1/+1 counter on it
5. Repeat

Results

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