Power Artifact, and Grim Monolith

Prerequisites

• Power Artifact on the battlefield
• Grim Monolith on the battlefield
• Power Artifact attached to Grim Monolith

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