They are worth five Golden Coins in all Mario games with the exception of Super Mario Sunshine. This means that their collection adds 5 to the coin counter. In Super Mario 64, Super Mario 64 DS blue coin switches can be depressed by a ground pound, which makes a number of blue coins appear for a short time. In Super Mario 64 and Super Mario 64 DS Blue Coins would also heal up to five units of health when collected.
In Super Mario Sunshine, Blue Coins become extremely valuable, as ten of them could be traded for a Shine Sprite. Also, Blue Coins would heal up to 3 units of health when collected. 30 blue coins are located in each world area.