Evil Twin + Felidar Guardian

Prerequisites

You have enough mana to cast Evil Twin.

Steps

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