Narset's Reversal, and Isochron Scepter

Prerequisites

• Narset's Reversal in exile
• Isochron Scepter on the battlefield
• plus enough mana to cast the extra turn spell each turn available

Steps

1. Cast the extra turn spell by paying its mana cost
2. Holding priority, activate Isochron Scepter by paying and tapping it, casting a copy of Narset's Reversal
3. Resolve the copy of Narset's Reversal, causing you to copy the extra turn spell, and return the original extra turn spell to your hand
4. Resolve the copy of the extra turn spell, causing you to take at least one extra turn after this one
5. Repeat each turn

Results

• Infinite turns