Voltaic Construct, Karn, Silver Golem, and Grim Monolith

Prerequisites

• Voltaic Construct on the battlefield
• Karn, Silver Golem on the battlefield
• Grim Monolith on the battlefield
• available

Steps

1. Animate Grim Monolith using Karn
2. Activate Grim Monolith by tapping it, adding
3. Activate Voltaic Construct by paying , untapping Grim Monolith
4. Repeat from step 2

Results

• Infinite colorless mana
• Infinite untap of artifact creatures you control