Quicksilver Gargantuan, and Felidar Guardian

Prerequisites

• Quicksilver Gargantuan in hand
• Felidar Guardian on the battlefield

Steps

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

Results

• Infinite LTB
• Infinite ETB