Voltaic Construct, Karn, the Great Creator, and Astral Cornucopia

Prerequisites

• Voltaic Construct on the battlefield
• Karn, the Great Creator on the battlefield
• Astral Cornucopia on the battlefield

Steps

1. Animate Astral Cornucopia using Karn, the Great Creator
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