Blue Coin

Blue Coins are a special type of coin that first appeared in Super Mario 64 and have since been featured in other games. Though their purpose varies between games, they usually serve as a more valuable type of coin.

Super Mario 64 / Super Mario 64 DS
Blue Coins made their first appearance in Super Mario 64 and also made an appearance in Super Mario 64 DS

In these games, Blue Coins are worth five Yellow Coins each. They can usually be found by Ground Pounding a Blue Switches, which will cause a number of Blue Coins to appear, but only for a limited amount of time. Blue Coins can also be collected by defeating tougher enemies, such as Koopa Troopas, Piranha Plants, Boos, Mr. Is, or Pokeys. Big Goombas also give out a Blue Coin if killed using a Ground Pound. Bookends will provide a Blue Coin when they are attacked, but not if they disappear after colliding with the floor, a wall, or the player.

Blue Coins are also found in the slides on Cool, Cool Mountain (one is present) and Tall, Tall Mountain (three are present), where they will start to move away from Mario once he gets close to them, in contrast to the stationary Yellow Coins. However, the Blue Coins in Tall, Tall Mountain are not present in Super Mario 64 DS.

Super Mario Sunshine
In Super Mario Sunshine, Blue Coins appear as a rare, collectable type of coin. There are 240 Blue Coins total in the game (30 in each of the seven courses, 20 in Delino Plaza and Delfino Airstrip, and 10 in Corona Mountain) By heading to the Boathouse located in the west part of Delfino Plaza, the player can trade ten Blue Coins for one Shine Sprite from the Raccoons running the store, meaning 24 Shine Sprites total are available using this method. They do not affect the number of Yellow Coins that Mario has collected, however, though they restore two health points when collected. The player receives the option to save their game for each Blue Coin they grab.

There are some Blue Coins (as well as Yellow Coins) in Sirena Beach's hotel that are fake since they do not spin and move. They are actually Boos with coins inside of them. If Mario gets too close to a "coin", the Boo appears.

New Super Mario Bros. Wii
Blue Coins appear in New Super Mario Bros. Wii, having the same role as Silver Coins from the first New Super Mario Bros. and Super Mario Bros. 3, appearing when Mario hits a P-Switch. When the player collects them all in a level before they disappear, the audience cheers. They are often arranged in patterns. Blue Coins also appear in New Super Mario Bros. 2 (but when the player collects them all, the audience instead claps) and New Super Mario Bros. U. In the latter game's expansion pack New Super Luigi U, a Blue Ring which produces many Blue Coins similar to P-Switches also appears.

Super Mario 3D World
Blue Coins reappear in Super Mario 3D World, where they serve the same function as in the New Super Mario Bros. series.

Mario Pinball Land
In Mario Pinball Land, these coins can be obtained by making a combo without using the flipper. Mario can use them to play minigames from Toad for Power Stars.

Mario & Sonic at the Olympic Winter Games (Wii)
In Mario & Sonic at the Olympic Winter Games, Blue Coins appear after the player buys the blue treasure chest in the Secret Shop. Getting all five Blue Coins will result in the player getting an emblem. The events that blue coins appear in are Dream Alpine, Dream Ski Jumping, Dream Ski Cross, Dream Snowboard Cross, Dream Short Track, and Dream Bobsleigh.

Super Smash Bros. for Nintendo 3DS
Blue Coins appear in the Golden Plains stage exclusive to Super Smash Bros. for Nintendo 3DS, after a fighter steps on a P-Switch that occasionally appears during a match. They serve the same function as the normal Coins in the stage.

Mario + Rabbids Kingdom Battle
In Mario + Rabbids Kingdom Battle, they appear in the bonus stages. Collecting all of the Blue Coins will reward the player with a new weapon.

Trivia

 * The functionality of Blue Coins in Super Mario 64 was likely carried over from the development of Super Mario World, as in that game Red Coins, which went unused, also awarded the player with five Yellow Coins when collected.