Dreamstone Hedron, Voltaic Construct, and Karn, Silver Golem

Prerequisites

• Dreamstone Hedron on the battlefield
• Voltaic Construct on the battlefield
• Karn, Silver Golem on the battlefield
• Dreamstone Hedron does not have summoning sickness
• available

Steps

1. Activate Karn by paying , causing Dreamstone Hedron to become an artifact creature until end of turn
2. Activate Dreamstone Hedron's first ability by tapping it, adding
3. Activate Voltaic Construct by paying , untapping Dreamstone Hedron
4. Repeat from step 2

Results

• Infinite colorless mana