Mikaeus, the Unhallowed, Phyrexian Altar, and River Kelpie

Prerequisites

• Mikaeus, the Unhallowed on the battlefield
• Phyrexian Altar on the battlefield
• River Kelpie on the battlefield

Steps

1. Activate Phyrexian 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 Phyrexian 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 colored mana
• Near-infinite death triggers
• Near-infinite ETB
• Near-infinite LTB
• Near-infinite sacrifice triggers