Karn, the Great Creator, Voltaic Construct, and Empowered Autogenerator

Prerequisites

• Karn, the Great Creator on the battlefield
• Voltaic Construct on the battlefield
• Empowered Autogenerator on the battlefield
• Empowered Autogenerator does not have summoning sickness
• Empowered Autogenerator has at least two charge counters on it

Steps

1. Activate Karn's first loyalty ability, causing Empowered Autogenerator to become an artifact creature until end of turn
2. Activate Empowered Autogenerator by putting a charge counter and tapping it, adding mana of any color equal to charge counters on Empowered Autogenerator
3. Activate Voltaic Construct by paying , untapping Empowered Autogenerator
4. Repeat from step 2

Results

• Infinite colored mana