How can you create a combo with Urza, Prince of Kroog, Timestream Navigator, Thran Forge?
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[START OF COMBO]This combo can be formed with Urza, Prince of Kroog, Timestream Navigator, Thran Forge

Color identity: WU
Mana cost: {10}{U}{U} each turn
Steps:
  1. Activate Thran Forge by paying {2}, causing Timestream Navigator to get +1/+0 and become an artifact until end of turn.
  2. Activate Urza by paying {6}, creating a token copy of Timestream Navigator that is a 1/1 Soldier creature.
  3. Activate the oldest Timestream Navigator by paying {2}{U}{U}, tapping it and putting it on the bottom of your library from the battlefield, causing you to take an extra turn after this one.
  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
  - You have the city's blessing.
  - Timestream Navigator does not have summoning sickness.
[END OF COMBO PREREQUISITES]
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