Grand Star Coin
From the Super Mario Wiki
A Grand Star Coin is a Skill Item in Puzzle & Dragons: Super Mario Bros. Edition. It raises the Skill levels of teammates whose Skill levels have reached level 4 using Star Coins such as most forms of Mario, and all types of Hammer Bros., Coin Coffers, Thwomps, and Whomps. Grand Star Coins can be obtained by opening up ? Blocks; winning them from the Lucky ? Blocks game in Toad Houses; or from defeating "Thwomp & Thwimps" and "Whomp & Boos" with a 10+ Combo attack.