These are the following ways to earn Stardust progress to unlock Stardust Challenge missions:

• Earn during Stardust Missions: Stardust Bottles can appear during "Stardust Mode" and can be collected from the board by clearing the bottle or by moving it to the bottom of the board.
•  During Stardust Mode (Blitz Mode within the Stardust Mission Feature) Stardust bottoles are added and award bonus Stardust as they are cleared during this mode.
• Popping Balloons after the game round during Stardust Missions will grant Stardust in lieu of Coins. Round balloons give Coins, Star-shaped Balloons give Stardust.
• If you are playing with an Emoji that is already at maximum level for Stardust, you may receive Token prizes instead at a percentage proportion to the prize.