Gilder Bairn, Agatha's Soul Cauldron, and Marwyn, the Nurturer

Prerequisites

• Gilder Bairn in exile
• Agatha's Soul Cauldron on the battlefield
• Marwyn, the Nurturer on the battlefield

Steps

1. Activate Marwyn by tapping it, adding at least Activate Marwyn using Gilder Bairn's ability by paying and untapping it, doubling the counters on target permanent
2. Repeat

Results

• Infinite green mana
• Infinite proliferate