Tenacious Dead, Phyrexian Altar, and Sifter of Skulls

Prerequisites

• Tenacious Dead on the battlefield
• Phyrexian Altar on the battlefield
• Sifter of Skulls on the battlefield

Steps

1. Activate Phyrexian Altar by sacrificing Tenacious Dead, adding
2. When Tenacious Dead dies, it and Sifter of Skulls trigger
3. Resolve the Sifter of Skulls trigger, creating a token
4. Activate that token by sacrificing it, adding
5. Resolve the Tenacious Dead trigger, paying to return it to the battlefield from your graveyard
6. Repeat
7. Activate Phyrexian Altar by sacrificing Tenacious Dead, adding
8. When Tenacious Dead dies, it and Pitiless Plunderer trigger
9. Resolve the Pitiless Plunderer trigger, creating a Treasure token
10. Activate that Treasure token by tapping and sacrificing it, adding
11. Resolve the Tenacious Dead trigger, paying to return it to the battlefield from your graveyard
12. Repeat

Results

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