Mikaeus, the Unhallowed, Ashnod's Altar, and Dream Seizer

Prerequisites

• Mikaeus, the Unhallowed on the battlefield
• Ashnod's Altar on the battlefield
• Dream Seizer on the battlefield

Steps

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

Results

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