Phantom Steed, Time Stretch, and Zealous Lorecaster

Prerequisites

• Phantom Steed on the battlefield
• Time Stretch in hand
• Zealous Lorecaster in exile
• each other turn available

Steps

1. Cast Time Stretch by paying its mana cost, causing you to take two extra turns after this one Declare Phantom Steed as an attacker
2. It triggers, creating a token copy of Zealous Lorecaster that's tapped and attacking
3. When the Zealous Lorecaster token enters, it triggers, returning Time Stretch from your graveyard to your hand
4. Repeat during your second extra turn

Results

• Infinite turns
• Lock