Mikaeus, the Unhallowed, Phyrexian Altar, and Putrid Goblin

Prerequisites

• Mikaeus, the Unhallowed on the battlefield
• Phyrexian Altar on the battlefield
• Putrid Goblin on the battlefield

Steps

1. Activate Phyrexian Altar by sacrificing Putrid Goblin
2. When Putrid Goblin dies, its persist ability triggers, returning it from your graveyard to the battlefield with a -1/-1 counter on it
3. Activate Phyrexian Altar by sacrificing Putrid Goblin
4. When Putrid Goblin 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 colored mana
• Infinite death triggers
• Infinite sacrifice triggers