How can you create a combo with Mythos of Illuna, Dual Casting, Retreat to Coralhelm?
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[START OF COMBO]This combo can be formed with Mythos of Illuna, Dual Casting, Retreat to Coralhelm

Color identity: GUR
Mana cost: {2}{U}{U}
Steps:
  1. Cast Mythos of Illuna by paying {2}{U}{U}, targeting any permanent.
  2. Holding priority, activate any Mountain you control by tapping it, adding {R}.
  3. Activate the creature with Dual Casting attached by paying {R} and tapping it, creating a copy of Mythos of Illuna targeting any basic Mountain you control.
  4. Resolve the Mythos of Illuna copy, creating a token copy of the basic Mountain.
  5. The basic Mountain token enters the battlefield, triggering Retreat to Coralhelm, untapping the creature with Dual Casting attached.
  6. Repeat from step 2.[END OF COMBO STEPS]

Result:
  - Infinite landfall triggers
  - Infinite magecraft triggers
  - Infinite tapped Mountain tokens[END OF COMBO RESULT][END OF COMBO]

Other prerequisites:
  - Mythos of Illuna must be in your hand
  - Dual Casting must be on the battlefield
  - Retreat to Coralhelm must be on the battlefield
  - Dual Casting attached to a creature that does not have summoning sickness.
  - You control at least one basic Mountain.
[END OF COMBO PREREQUISITES]
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