Phyrexian Altar, Twilight Shepherd, and Thran Vigil

Prerequisites

• Phyrexian Altar on the battlefield
• Twilight Shepherd on the battlefield
• Thran Vigil on the battlefield

Steps

1. Activate Phyrexian Altar by sacrificing Twilight Shepherd
2. When Twilight Shepherd dies, its persist ability triggers, returning it from your graveyard to the battlefield with a -1/-1 counter on it
3. Thran Vigil triggers, putting a +1/+1 counter on Twilight Shepherd
4. Repeat

Results

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