Cavalier of Night, Activated Sleeper, and Phyrexian Altar

Prerequisites

• Cavalier of Night on the battlefield
• Activated Sleeper in the graveyard
• Phyrexian Altar on the battlefield

Steps

1. Activate Phyrexian Altar by sacrificing Cavalier of Night, adding one mana of any color
2. When Cavalier of Night dies, it triggers, returning Activated Sleeper from your graveyard to the battlefield as a copy of Cavalier of Night
3. When Activated Sleeper enters the battlefield, it triggers; choose not to sacrifice a creature
4. Activate Phyrexian Altar by sacrificing Activated Sleeper, adding one mana of any color
5. When Activated Sleeper dies, it triggers, returning Activated Sleeper from your graveyard to the battlefield as a copy of Cavalier of Night
6. Repeat from step 3

Results

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