Voltaic Construct + Silverskin Armor + Gumato

Voltaic Construct

Silverskin Armor

Gumato

How it works

1. Activate Gumato by tapping it, adding
2. Activate Voltaic Construct by paying 2, untapping Gumato.
3. Repeat

By outfitting Gumato with Silverskin Armor, we transform our green mana-producer into an artifact creature, making it a legal target for Voltaic Construct's untap ability. Since Gumato has vigilance, attacking doesn't tap it, leaving it free to tap for three green mana while Voltaic Construct only demands two mana to untap it. We use a portion of the green mana generated by Gumato to pay the {2} activation cost of Voltaic Construct, netting a positive surplus of mana with every iteration.