Voltaic Construct + Ashnod's Transmogrant + Karametra's Acolyte

Voltaic Construct

Ashnod's Transmogrant

Karametra's Acolyte

How it works

1. Cause Karametra's Acolyte to become an artifact using Ashnod's Transmogrant.
2. Activate Karametra's Acolyte by tapping it, adding at least .
3. Activate Voltaic Construct by paying 2, untapping Karametra's Acolyte.
4. Repeat from step 2.

To set this engine in motion, Ashnod's Transmogrant turns Karametra's Acolyte into an artifact creature, allowing it to be legally targeted by Voltaic Construct's untap ability. Once the Acolyte is properly typed and your devotion to green produces at least three green mana per tap, you simply use a portion of that floating mana to pay the {2} activation cost for Voltaic Construct. This untaps Karametra's Acolyte so you can tap it again, looping the process to generate infinite green mana.