Gigantoplasm + Felidar Guardian

Prerequisites

You have enough mana to cast Gigantoplasm.

Steps

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