Altaïr Ibn-La'Ahad, Medomai the Ageless, and Roshan, Hidden Magister

Prerequisites

• Altaïr Ibn-La'Ahad on the battlefield
• Medomai the Ageless in the graveyard
• Roshan, Hidden Magister on the battlefield
• An opponent cannot block creatures you control

Steps

1. Declare Altaïr Ibn-La'Ahad as an attacker
2. Altaïr Ibn-La'Ahad triggers, exiling Medomai the Ageless from your graveyard with a memory counter on it as it is an Assassin due to Maskwood Nexus, and then creating a tapped and attacking token copy of each creature you own in exile with a memory counter on it
3. Deal combat damage to an opponent using the Medomai the Ageless token
4. The Medomai the Ageless token triggers, causing you to take an extra turn after this one
5. At the end of your combat phase, Altaïr Ibn-La'Ahad triggers, exiling the Medomai the Ageless token
6. During the combat phase of your extra turn, declare Altaïr Ibn-La'Ahad as an attacker
7. Altaïr Ibn-La'Ahad triggers, creating a tapped and attacking token copy of each creature you own in exile with a memory counter on it
8. Repeat from step 3

Results

• Infinite extra turns