Voltaic Key + Rings of Brighthearth + Astral Cornucopia

Prerequisites

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Steps

1. 1Activate Astral Cornucopia by tapping it, adding at least four mana of any color.
2. 2Activate Voltaic Key by paying and tapping it, targeting itself.
3. 3Rings of Brighthearth triggers, causing you to pay to copy Voltaic Key's ability, targeting Astral Cornucopia.
4. 4Resolve both Voltaic Key abilities, untapping it and Astral Cornucopia.
5. 5Repeat.

Effects

• Infinite colored mana
• Infinite mana artifacts you control can produce
• Infinite untap of artifacts you control