Yore-Tiller Nephilim, Medomai the Ageless, and Altar of Dementia

Prerequisites

• Yore-Tiller Nephilim on the battlefield
• Medomai the Ageless in the graveyard
• Altar of Dementia on the battlefield

Steps

1. Declare Yore-Tiller Nephilim as an attacker
2. Yore-Tiller Nephilim triggers, returning Medomai from your graveyard to the battlefield tapped and attacking
3. Deal combat damage using Medomai, triggering its ability, causing you to take an extra turn after this one
4. Activate Altar of Dementia by sacrificing Medomai
5. Repeat each turn

Results

• Infinite turns
• Lock