Voltaic Construct + Sanctum Weaver + Encroaching Mycosynth

Voltaic Construct

Sanctum Weaver

Encroaching Mycosynth

How it works

1. Activate Sanctum Weaver by tapping it, adding at least 3.
2. Activate Voltaic Construct by paying 2, untapping Sanctum Weaver.
3. Repeat

The secret engine driving this loop is Encroaching Mycosynth, which turns all of your nonland permanents into artifacts—including the crucial Sanctum Weaver. Because Sanctum Weaver is now an artifact in addition to its enchantment type, it qualifies as an artifact creature when you make it one, or more importantly, it becomes a valid target for Voltaic Construct's ability. As long as you control at least three total enchantments, tapping Sanctum Weaver generates more than enough mana to pay the {2} activation cost required for Voltaic Construct to untap it, leaving you with an unstoppable surplus of infinite colored mana.