Basalt Monolith, March of the Machines, and Agatha of the Vile Cauldron

Prerequisites

• Basalt Monolith on the battlefield
• March of the Machines on the battlefield
• Agatha of the Vile Cauldron on the battlefield

Steps

1. Activate Basalt Monolith's first ability by tapping it, adding
2. Activate Basalt Monolith's last ability by paying at most , untapping it
3. Repeat

Results

• Infinite colorless mana