Deathrender, Gravedigger, Eternal Witness, and Ashnod's Altar

Prerequisites

• Deathrender on the battlefield
• Gravedigger in hand
• Eternal Witness on the battlefield
• Ashnod's Altar on the battlefield
• Deathrender attached to Eternal Witness

Steps

1. Activate Ashnod's Altar by sacrificing Eternal Witness, adding
2. Eternal Witness dies, triggering Deathrender, putting Gravedigger from your hand onto the battlefield and attaching Deathrender to it
3. Gravedigger enters the battlefield, returning Eternal Witness from your graveyard to your hand
4. Activate Ashnod's Altar by sacrificing Gravedigger, adding
5. Gravedigger dies, triggering Deathrender, putting Eternal Witness from your hand onto the battlefield and attaching Deathrender to it
6. Eternal Witness enters the battlefield, returning Gravedigger from your graveyard to your hand
7. Repeat

Results

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