Karn, the Great Creator, Voltaic Construct, and Nyx Lotus

Prerequisites

• Karn, the Great Creator on the battlefield
• Voltaic Construct on the battlefield
• Nyx Lotus on the battlefield
• Nyx Lotus does not have summoning sickness
• You have more than three devotions of one color

Steps

1. Activate Karn's first loyalty ability, causing Nyx Lotus to become an artifact creature until end of turn
2. Activate Nyx Lotus by tapping it, adding mana of that color equal to your devotion of that color
3. Activate Voltaic Construct by paying , untapping Nyx Lotus
4. Repeat from step 2

Results

• Infinite colored mana