Karn, the Great Creator, Voltaic Construct, and Basalt Monolith

Prerequisites

• Karn, the Great Creator on the battlefield
• Voltaic Construct on the battlefield
• Basalt Monolith on the battlefield
• Basalt Monolith does not have summoning sickness

Steps

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

Results

• Infinite colorless mana