Donatello, Mutant Mechanic + Grim Monolith + Voltaic Construct

U identity

Commander legal

The 3 combo pieces

• Donatello, Mutant Mechanic
• Grim Monolith
• Voltaic Construct

How to execute it

1. Animate Grim Monolith using Donatello.
2. Activate Grim Monolith by tapping it, adding {C}{C}{C}
3. Activate Voltaic Construct by paying {2}, untapping Grim Monolith.
4. Repeat from step 2.

What the combo produces

• Infinite colorless mana
• Infinite untap of artifact creatures you control