Wormfang Manta, Roon of the Hidden Realm, and Doorkeeper Thrull

Prerequisites

• Wormfang Manta on the battlefield
• Roon of the Hidden Realm on the battlefield
• Doorkeeper Thrull on the battlefield
• each turn available

Steps

1. Blink Wormfang Manta using Roon of the Hidden Realm
2. Wormfang Manta's first ability won't trigger due to Doorkeeper Thrull
3. Wormfang Manta's second ability triggers, causing you to take an extra turn after this one
4. Repeat each turn

Results

• Infinite turns
• Lock