Time Vault, and Teferi, Timebender

Prerequisites

• Time Vault on the battlefield
• Teferi, Timebender on the battlefield

Steps

1. Activate Teferi's first loyalty ability by putting two loyalty counters on it, untap Time Vault
2. Activate Time Vault by tapping it, causing you to take an extra turn after this one
3. Repeat each turn

Results

• Infinite turns