How can you create a combo with Retrofitter Foundry, Mana Echoes?
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[START OF COMBO]This combo can be formed with Retrofitter Foundry, Mana Echoes

Color identity: R
Mana cost: {2} plus up to {10} additional depending on the number of Servos you control
Steps:
  1. Activate Retrofitter Foundry's second ability by paying {2} and tapping it, creating a 1/1 Servo artifact creature token.
  2. When the Servo enters the battlefield, Mana Echoes triggers.
  3. If you control less than three Servos, activate Retrofitter Foundry's first ability by paying {3}, untapping it.
  4. If you control less than three Servos, repeat from step 1 until you control three Servos.
  5. Resolve all Mana Echoes triggers, adding {C} for each Servo you control for each trigger.
  6. Activate Retrofitter Foundry's first ability by paying {3}, untapping it.
  7. Activate Retrofitter Foundry's second ability by paying {2} and tapping it, creating a 1/1 Servo artifact creature token.
  8. When the Servo enters the battlefield, Mana Echoes triggers, adding {C} for each Servo you control.
  9. Repeat from step 6.
  10. Once you have infinite mana, you may use Retrofitter Foundry's other abilities.[END OF COMBO STEPS]

Result:
  - Infinite leaves the battlefield
  - Infinite enters the battlefield
  - Infinite sacrifice triggers
  - Infinite death triggers
  - Infinite creature tokens[END OF COMBO RESULT][END OF COMBO]

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