Grim Monolith, and Nyxbloom Ancient

Prerequisites

• Grim Monolith on the battlefield
• Nyxbloom Ancient on the battlefield

Steps

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

Results

• Infinite colorless mana