Dreamstone Hedron, Voltaic Construct, and Karn, the Great Creator

Prerequisites

• Dreamstone Hedron on the battlefield
• Voltaic Construct on the battlefield
• Karn, the Great Creator on the battlefield
• Dreamstone Hedron does not have summoning sickness

Steps

1. Activate Karn's first ability by putting a loyalty counter on it, 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