Prototype Portal, Ugin's Nexus, and Arcbound Ravager

Prerequisites

• Prototype Portal on the battlefield
• Ugin's Nexus in exile
• Arcbound Ravager on the battlefield
• each turn available

Steps

1. Activate Prototype Portal by paying and tapping it, creating a token copy of Ugin's Nexus
2. Activate Arcbound Ravager by sacrificing the Ugin's Nexus token
3. The Ugin's Nexus token is exiled instead of being put into your graveyard, causing you to take an extra turn after this one
4. Resolve the Arcbound Ravager ability, putting a +1/+1 counter on it
5. Repeat each turn

Results

• Infinite turns