Diamond

Diamonds are real-world precious gemstones that appear in various roles in the Mario franchise and related series, often as a collectible item. They are also the namesake of various other objects and locations.

Mario is Missing!
When Luigi visits Amsterdam in the PC version of Mario is Missing!, he finds that, like every other city in the game, Koopa Troopas have stolen precious artifacts from its landmarks, including a diamond from the Amsterdam Diamond Center. Luigi has to track it down and return it to the Center after proving its authenticity by answering trivia questions.

Wario's Woods
Diamonds appear in both versions of Wario's Woods whenever Toad takes out four or more enemies with a single bomb. They appear in all the same colors that bombs do, and can be similarly picked up and placed down to eliminate enemies of the same color. When this occurs, however, not only does the player get a sizable point bonus, but every other enemy of that color, regardless of position, is also eliminated.

Wario Land 4
Diamonds are an optional collectible item in Wario Land 4. They are worth 1,000 points, which in this game can be spent in the Mini-Game Shop. They are usually located throughout a level in secret or hard-to-reach areas. They can also be found in pink areas.

Wario Land: Shake It!
Diamonds also appear in Wario Land: Shake It!, behaving similarly to their appearance in Wario Land 4. They are now worth 10,000 points.

Wario World
Red diamonds appear in each level of Wario World, wherein they must be gathered from trapdoors to cause the Stone Doohickey blocking the way to the boss to vanish.

Additionally, a more typical diamond appears as a treasure, located in the pink treasure chest in Greenhorn Forest.

Luigi's Mansion
Various types of diamonds appear as rare collectibles in Luigi's Mansion.

Luigi's Mansion: Dark Moon
Diamonds are the fifth set of Gems in Luigi's Mansion: Dark Moon, with thirteen being hidden in the Treacherous Mansion.

Mario Party: Island Tour
Two minigames in Mario Party: Island Tour have the goal of collecting diamonds.

In Cheep Diamonds, varying amounts of diamonds are eaten by Cheep Chomps, and players must choose the one that ate the most.

Diamond a Dozen has five holes with diamonds inside, which players are given a brief view of at the start of the minigame. They must keep track of how many diamonds each hole had, and be the first to pick the one with the most.

Captain Toad: Treasure Tracker
Captain Toad: Treasure Tracker features collectible items known as Super Gems, which resemble diamonds and are referred to as "Super Diamonds" in languages other than English and German.

Dr. Mario World
Diamonds are the premium currency of Dr. Mario World, mainly used to summon new doctors, assistants, and single-use items. They can also be used to purchase more hearts if the player runs out, to give the player more capsules if they run out in a certain level, to give the player more time in challenge levels, or to start a level with a completely-filled skill meter. Another way to spend diamonds is through referrals (introduced in version 2.0.0), which cost 100 diamonds in exchange for that specific doctor.

Diamonds were usually purchased via real money, though there are some instances in which Diamonds may be collected for free during gameplay. As of July 28, 2021, diamonds are no longer available for purchase.