Clever Impersonator, and Felidar Guardian

Prerequisites

• Clever Impersonator in hand
• Felidar Guardian on the battlefield

Steps

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

Results

• Infinite ETB
• Infinite LTB