River Kelpie, Mikaeus, the Unhallowed, and Altar of Dementia

Prerequisites

• River Kelpie on the battlefield
• Mikaeus, the Unhallowed on the battlefield
• Altar of Dementia on the battlefield

Steps

1. Activate Altar of Dementia by sacrificing River Kelpie
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. Resolve the Altar of Dementia trigger, causing target player to mill cards equal to River Kelpie's power
7. Activate Altar of Dementia by sacrificing River Kelpie
8. River Kelpie's undying and persist abilities trigger
9. Resolve the undying trigger, returning River Kelpie from your graveyard to the battlefield with a +1/+1 counter on it
10. River Kelpie enters the battlefield, causing you to draw a card
11. The persist trigger fails to resolve because River Kelpie is not in your graveyard
12. Resolve the Altar of Dementia trigger, causing target player to mill cards equal to River Kelpie's power
13. Repeat

Results

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