River Song, Conjurer's Bauble, Prototype Portal, and Walk the Aeons

Prerequisites

• River Song on the battlefield
• Conjurer's Bauble in exile
• Prototype Portal on the battlefield
• Walk the Aeons in hand
• plus enough mana to cast the extra turn spell each turn available

Steps

1. Activate Prototype Portal by paying and tapping it, creating a token copy of Conjurer's Bauble
2. Cast Walk the Aeons by paying its mana cost, causing you to take an extra turn after this one
3. Activate the Conjurer's Bauble token by tapping and sacrificing it, putting Walk the Aeons onto the bottom of your library from your graveyard, and then causing you to draw Walk the Aeons from the bottom of your library due to River Song
4. Repeat each turn

Results

• Infinite turns