Does anyone know when or how the cards show up?

Does anyone know when or how the cards show up? - Crop woman showing pop up gift card with decorative heart

Infinite Dreams has added a new feature to the game in the latest update. Cards are like bonus achievements for your plane. I can't find any pattern when or how they appear (if one exists). Did anyone ever find something like a pattern on their appearance?

achievements sky-force-2014

Pictures about "Does anyone know when or how the cards show up?"

Does anyone know when or how the cards show up? - Man in White Shirt and Black Hat Holding Deck of Cards

Does anyone know when or how the cards show up? - Closeup from above of white paper card composed on rows of delicious caramel gummy jelly sweets in modern candy shop

Does anyone know when or how the cards show up? - Brown Wooden Framed Picture of a Woman

WHEN YOU SHOW YOUR MOM YOUR REPORT CARD

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Images: Michelle Leman, Tima Miroshnichenko, Karolina Grabowska, cottonbro