From the Super Mario Wiki
Blue Paratroopas are a group of three blue-shelled Koopa Paratroopas in Mario & Luigi: Bowser's Inside Story. Mario and Luigi first encounter the trio after they hit the giant Blue Shell Block. After some quick arguing, the leader of the Blue Paratroopas silences them and tells Mario that the Blue Shell fits him nicely. The leader teaches the Mario Bros. how to use Shell Mario with a training exercise. After completing the exercise, the Mario Bros. are awarded all the Attack Pieces for Yoo Who Cannon.
The Mario Bros. encounter the Blue Paratroopas again in the lower eastern portion of Peach's Castle Grounds. Mario and Luigi hit an Attack Piece Block which contained seven Attack Pieces. As a result, the trio flies over and argues about who the Attack Pieces belong to. The leader of the Blue Paratroopas then decides to settle the argument with a payment of 30 coins. When Mario and Luigi reply that 30 coins isn't much, the leader raises the fee to 300 coins. The other two Blue Paratroopas get stunned at the high amount. The leader then compensates for the high fee by telling the Mario Bros. where the remaining three Attack Pieces are and circles the locations on the map. The leader also hints that the Attack Piece Blocks are invisible.