Deepfathom Echo, and Felidar Guardian

Prerequisites

• Deepfathom Echo in hand
• Felidar Guardian on the battlefield

Steps

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

Results

• Infinite LTB
• Infinite ETB