Myr Welder + Voltaic Construct + Prismatic Geoscope

Myr Welder

Voltaic Construct

Prismatic Geoscope

How it works

1. Activate Myr Welder using Prismatic Geoscope's ability by tapping it, adding at least three mana of any color.
2. If Voltaic Construct is on the battlefield, activate Voltaic Construct by paying 2, untapping Myr Welder. Otherwise, activate Myr Welder using Voltaic Construct's ability by paying 2, untapping Myr Welder.
3. Repeat.

This loop transforms Myr Welder into a self-sustaining mana and untap engine by absorbing the activated abilities of both its peers from the graveyard. While Prismatic Geoscope provides the domain-fueled engine to generate a surplus of colored mana with every tap, Voltaic Construct acts as the catalyst that pays a portion of that mana to constantly untap the Welder. Because Myr Welder can freely copy the Construct's ability once it is exiled, you can endlessly cycle the untap and tap sequence to net infinite colored mana and infinite untaps of your artifact creatures.