Voltaic Construct + Encroaching Mycosynth + Bighorner Rancher

Voltaic Construct

Encroaching Mycosynth

Bighorner Rancher

How it works

1. Activate Bighorner Rancher by tapping it, adding at least 3.
2. Activate Voltaic Construct by paying 2, untapping Bighorner Rancher.
3. Repeat

This clever engine transforms Bighorner Rancher into a self-sustaining mana fountain by leveraging Encroaching Mycosynth to turn all of your nonland permanents into artifacts. Because Encroaching Mycosynth changes its types, Bighorner Rancher counts as an artifact creature, making it a legal target for Voltaic Construct's untap ability. As long as the Rancher's power is 3 or greater—allowing its tap ability to yield more green mana than the {2} cost required by Voltaic Construct—you can endlessly loop these activations to generate infinite green mana and infinite untaps.