How can you create a combo with Felidar Guardian, Altar of the Brood, Spark Double?
user
[START OF COMBO]This combo can be formed with Felidar Guardian, Altar of the Brood, Spark Double

Color identity: WU
Mana cost: {3}{U}
Steps:
  1. Cast Spark Double by paying {3}{U}.
  2. Spark Double enters the battlefield as a copy of Felidar Guardian, triggering Altar of the Brood and itself.
  3. Resolve the Altar of the Brood trigger, causing each opponent to mill a card.
  4. Resolve the Spark Double's trigger, blinking Felidar Guardian.
  5. Felidar Guardian enters the battlefield, triggering Altar of the Brood and itself.
  6. Resolve the Altar of the Brood trigger, causing each opponent to mill a card.
  7. Resolve the Felidar Guardian's trigger, blinking Spark Double.
  8. Repeat from step 2.[END OF COMBO STEPS]

Result:
  - Infinite enters the battlefield
  - Infinite leaves the battlefield
  - Infinite mill[END OF COMBO RESULT][END OF COMBO]

Other prerequisites:
  - Felidar Guardian must be on the battlefield
  - Altar of the Brood must be on the battlefield
  - Spark Double must be in your hand
[END OF COMBO PREREQUISITES]
assistant