Phyrexian Metamorph + Felidar Guardian

Prerequisites

You have enough mana to cast Phyrexian Metamorph.

Steps

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