Undercover Operative + Felidar Guardian

Prerequisites

You have enough mana to cast Undercover Operative.

Steps

1. Cast Undercover Operative by paying its mana cost, choosing to have it enter the battlefield as a copy of Felidar Guardian
2. When Undercover Operative enters the battlefield, it triggers, blinking Felidar Guardian.
3. When Felidar Guardian enters the battlefield, it triggers, blinking Undercover Operative. Choose to have Undercover Operative enter the battlefield as a copy of Felidar Guardian.
4. Repeat from step 2.