Voltaic Construct + Empowered Autogenerator + The Blackstaff of Waterdeep

Voltaic Construct

Empowered Autogenerator

The Blackstaff of Waterdeep

How it works

1. Animate Empowered Autogenerator using The Blackstaff of Waterdeep.
2. Activate Empowered Autogenerator by tapping it, putting a charge counter on it and adding 1 for each charge counter on it.
3. Activate Voltaic Construct by paying 2, untapping Empowered Autogenerator.
4. Repeat from step 2.

To get this engine running, you first need The Blackstaff of Waterdeep to animate Empowered Autogenerator, turning it into a 4/4 artifact creature so it's a valid target for untapping effects. Once transformed, tapping Empowered Autogenerator adds a scaling amount of mana based on its growing charge counters, which directly fuels the activation cost of Voltaic Construct. Because Voltaic Construct untaps the Autogenerator for just two mana, you'll net a surplus of mana with every iteration once the counter count gets high enough, letting you loop the process infinitely.