How can you create a combo with Doubling Cube, Voltaic Key, Rings of Brighthearth?
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[START OF COMBO]This combo can be formed with Doubling Cube, Voltaic Key, Rings of Brighthearth

Color identity: C
Mana cost: {10}
Steps:
  1. Float {10} mana in your mana pool.
  2. Activate Doubling Cube by paying {3} and tapping it, causing you to add {7}.
  3. Activate Voltaic Key by paying {1} and tapping it, targeting Doubling Cube.
  4. Rings of Brighthearth triggers, causing you to pay {2} to copy Voltaic Key's ability, targeting Voltaic Key.
  5. Resolve both Voltaic Key abilities, untapping Voltaic Key and Doubling Cube.
  6. Repeat from step 2.[END OF COMBO STEPS]

Result:
  - Infinite mana artifacts you control can produce
  - Infinite mana permanents you control can produce
  - Infinite untap of artifacts you control[END OF COMBO RESULT][END OF COMBO]

Other prerequisites:
  - All permanants must be on the battlefield
[END OF COMBO PREREQUISITES]
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