How can you create a combo with River Song, Timestream Navigator?
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[START OF COMBO]This combo can be formed with River Song, Timestream Navigator

Color identity: UR
Mana cost: {3}{U}{U}{U} each turn
Steps:
  1. During your upkeep, activate Timestream Navigator by paying {2}{U}{U}, tapping it and putting it on the bottom of your library, causing you to take an extra turn after this one.
  2. Move to your draw step, drawing Timestream Navigator from the bottom of your library due to River Song.
  3. Cast Timestream Navigator by paying {1}{U}.
  4. Repeat each turn.[END OF COMBO STEPS]

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

Other prerequisites:
  - All permanants must be on the battlefield
  - Timestream Navigator does not have summoning sickness.
  - You have the city's blessing.
[END OF COMBO PREREQUISITES]
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