Chameleon, Master of Disguise + Felidar Guardian

Steps

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