Infinite mana of colors among permanents you controlInfinite untap of artifact creatures you control
How it works
Cause Faeburrow Elder to become an artifact using Ashnod's Transmogrant.
Activate Faeburrow Elder by tapping it, adding at least 3.
Activate Voltaic Construct by paying 2, untapping Faeburrow Elder.
Repeat from step 2.
By turning Faeburrow Elder into an artifact with Ashnod's Transmogrant, we bridge the gap between our mana producer and our untap engine. This allows Voltaic Construct to repeatedly untap the Elder for just two mana. Because Faeburrow Elder taps to generate at least three mana of any color among our permanents, this loop easily pays for its own activation while leaving a surplus of infinite colored mana.