Prototype Portal, Ugin's Nexus, and Phantom Train

Prerequisites

• Prototype Portal on the battlefield
• Ugin's Nexus in exile
• Phantom Train 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 Phantom Train by acrificing 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 Phantom Train ability Repeat each turn

Results

• Infinite turns