Gilder Bairn, Agatha's Soul Cauldron, and Bighorner Rancher

Prerequisites

• Gilder Bairn in exile
• Agatha's Soul Cauldron on the battlefield
• Bighorner Rancher on the battlefield

Steps

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

Results

• Infinite green mana
• Infinite proliferate