Mikaeus, the Unhallowed, Umbral Collar Zealot, and River Kelpie

Prerequisites

• Mikaeus, the Unhallowed on the battlefield
• Umbral Collar Zealot on the battlefield
• River Kelpie on the battlefield

Steps

1. Activate Umbral Collar Zealot by sacrificing River Kelpie
2. When River Kelpie dies, its persist ability triggers, returning it from your graveyard to the battlefield with a -1/-1 counter on it
3. When River Kelpie enters, its first ability triggers, causing you to draw a card
4. Resolve the Umbral Collar Zealot ability
5. Activate Umbral Collar Zealot by sacrificing River Kelpie
6. When River Kelpie dies, its undying ability triggers, returning it from your graveyard to the battlefield with a +1/+1 counter on it
7. When River Kelpie enters, its first ability triggers, causing you to draw a card
8. Resolve the Umbral Collar Zealot ability
9. Repeat

Results

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