Voltaic Construct, Karn, Silver Golem, and Astral Cornucopia

Prerequisites

• Voltaic Construct on the battlefield
• Karn, Silver Golem on the battlefield
• Astral Cornucopia on the battlefield
• available

Steps

1. Animate Astral Cornucopia using Karn
2. Activate Astral Cornucopia by tapping it, adding at least three mana of any color Activate Voltaic Construct by paying , untapping Astral Cornucopia
3. Repeat from step 2

Results

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