River Kelpie, Mikaeus, the Unhallowed, and Ashnod's Altar

Prerequisites

• River Kelpie on the battlefield
• Mikaeus, the Unhallowed on the battlefield
• Ashnod's Altar on the battlefield

Steps

1. Activate Ashnod's Altar by sacrificing River Kelpie, adding
2. River Kelpie's persist and undying abilities trigger
3. Resolve the persist trigger, returning River Kelpie from your graveyard to the battlefield with a -1/-1 counter on it
4. River Kelpie enters the battlefield, causing you to draw
5. The undying trigger fails to resolve because River Kelpie is not in your graveyard
6. Activate Ashnod's Altar by sacrificing River Kelpie, adding
7. River Kelpie's undying and persist abilities trigger
8. Resolve the undying trigger, returning River Kelpie from your graveyard to the battlefield with a +1/+1 counter on it
9. River Kelpie enters the battlefield, causing you to draw a card
10. The persist trigger fails to resolve because River Kelpie is not in your graveyard
11. Repeat

Results

• Infinite card draw
• Near-infinite colorless mana
• Near-infinite death triggers
• Near-infinite ETB
• Near-infinite LTB
• Near-infinite sacrifice triggers