Requires

Phantom Steed must be on the battlefield. Walk the Aeons must be in hand. Eternal Witness must be in exile (exiled by Phantom Steed). An opponent can not block Phantom Steed. Mana needed:

Steps

1. Cast Walk the Aeons, taking an extra turn after this one.
2. Attack with Phantom Steed.
3. Phantom Steed triggers, creating a token copy of Eternal Witness that is tapped and attacking.
4. Eternal Witness enters, returning Walk the Aeons from your graveyard to your hand.
5. Pass the turn.
6. Repeat.

Results