How can you create a combo with The Sixth Doctor, Ugin's Nexus, Vedalken Mastermind, Krark-Clan Ironworks?
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[START OF COMBO]This combo can be formed with The Sixth Doctor, Ugin's Nexus, Vedalken Mastermind, Krark-Clan Ironworks

Color identity: GU
Mana cost: {5}{U} each turn
Steps:
  1. Cast Ugin's Nexus by paying {5}.
  2. The Sixth Doctor triggers, copying the Ugin's Nexus spell, with the copy being nonlegendary.
  3. Resolve both Ugin's Nexus spells.
  4. Activate Vedalken Mastermind by paying {U} and tapping it, returning the nontoken Ugin's Nexus to your hand.
  5. Activate Krark-Clan Ironworks by sacrificing the Ugin's Nexus token, adding {C}{C}.
  6. The Ugin's Nexus token is exiled instead of being put into your graveyard, causing you to take an extra turn after this one.
  7. Repeat each turn.[END OF COMBO STEPS]

Result:
  - Infinite turns[END OF COMBO RESULT][END OF COMBO]

Other prerequisites:
  - The Sixth Doctor must be on the battlefield
  - Ugin's Nexus must be in your hand
  - Vedalken Mastermind must be on the battlefield
  - Krark-Clan Ironworks must be on the battlefield
  - Vedalken Mastermind does not have summoning sickness.
[END OF COMBO PREREQUISITES]
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