Voltaic Construct + Ashnod's Transmogrant + Marwyn, the Nurturer

Voltaic Construct

Ashnod's Transmogrant

Marwyn, the Nurturer

How it works

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

This elegant machinery transforms Marwyn, the Nurturer into a self-sustaining mana engine by permanently turning her into an artifact with Ashnod's Transmogrant. Once she carries that artifact type, Voltaic Construct can repeatedly untap her using a portion of the green mana she generates. As long as Marwyn's power is at least 3, tapping her for mana easily pays the {2} activation cost to untap her while leaving pure profit behind, resulting in infinite green mana for whatever spells you need to cast.