Wish

A wish is the embodiment of a strong hope or desire for something to occur. The power of wishes is one of the strongest forces acting upon Mushroom World and its various related worlds. While anyone can make a wish, the ability to grant that wish usually resides within a powerful being, artifact, or location. However, the power of certain wish-granting sources is directly dependent on the conviction of the individual making the wish.

Background
The power of wishes has existed in some form since the beginning of time. The wish-granting beings known as the Star Spirits and their powerful artifact the Star Rod have apparently been around since time itself first began. According to Eldstar, the seven Star Spirits have "cared for the Star Rod since the beginning of time." The Star Spirits and the Star Rod reside in Star Haven high above the world. For countless millennia the Star Spirits have watched over the world, granting wishes to deserving people, thus allowing the world to prosper peacefully. How the Star Road is connected to these events is unknown. It's plausible that when a wish is made, the Star Road transforms them into Wish Stars, which, in turn, tell the wisher's desire to the Star Spirits who will then use the Star Rod to grant the wish if they deem it worth granting.

Super Mario RPG: Legend of the Seven Stars
During the events of Super Mario RPG: Legend of the Seven Stars, the power of wishes was threatened after the fracturing of the Star Road by the Smithy Gang. When Smithy invaded Mario's world, his minion Exor crashed through the Star Road, breaking off seven Star Pieces which fell to earth. Without these fragments, the Star Road was unable to transform wishes into Wish Stars and later grant them. Additionally, wishes that had been transformed into stars continued to fall to Star Hill, but since the Star Road was destroyed, these wishes were not granted. As such, a warrior of the Star Road named ♥♪!? (or "Geno" after the doll he inhabited) was sent to find the broken Star Pieces and restore the Star Road. Geno teamed up with Mario and his new ally Mallow in order to stop the Smithy Gang, collect the seven Star Pieces, and restore the power of wishes to the world. As Geno told Mario after collecting their second Star Piece: "The way things stand, yours is a world where wishes can't come true anymore."

Ultimately Mario, with the help of Geno, Mallow, Princess Peach, and Bowser, was able to collect six Star Pieces and confront Smithy, who had the last Star Piece in his possession. Before the battle, Smithy was informed about the power of wishes and the importance of the Star Pieces. The leader of the Smithy Gang therefore kept the last Star Piece in his possession to prevent anyone from restoring the power of wishes to the world, as that would directly interfere with his ability to conquer the world. He stated upon being confronted by Mario and his allies: "Why don't YOU give me YOUR stars. Why, then I could easily conquer this world! Then we could get rid of all wishes, and create a world filled with...WEAPONS!!" Smithy intended to replace wishes with his own weapons as one of the dominant forces in the world. Essentially, wishes were a threat to Smithy, as their power could assist those who did not have the weapons to resist his invasion. In the end however, Smithy was destroyed in battle and Mario was able to repair the Star Road with the seven Star Pieces. The power of wishes was restored to the world.

Paper Mario
During the events of Paper Mario, the power of wishes was co-opted by Bowser after the King of Koopas was able to secure the Star Rod for his own purposes. Bowser and his armies attacked Star Haven, sealing the Star Spirits inside magical cards and stealing the wish-granting Star Rod. The King of the Koopas decided to steal the Star Rod in order to grant his own wishes after years of having his personal wishes denied. While the Star Spirits receive many wishes from people on the surface, they do not grant every wish they receive, only those wishes of people they deemed deserving. The elder stars do not grant selfish wishes, such as Bowser's desire to "trounce Mario" or his hope for "Princess Peach to like me." However, after capturing the Star Rod, Bowser could use the Star Rod to turn himself into an invulnerable, all-powerful being. With the power of the Star Rod, Bowser was able to capture Princess Peach, conquer much of the Mushroom Kingdom, and finally defeat his nemesis Mario in battle (although Mario survived the confrontation, albeit barely).

Ultimately, Mario was able to revive the Star Spirits and used their power to negate the effects of the Star Rod. Mario was then able to defeat Bowser, and the authority to grant wishes via the Star Rod was returned to the Star Spirits.

Characteristics
The exact mechanisms by how a wish is granted is dependent on who or what is making the wish come true.

Stars, Star Kids and Star Spirits
The creatures known as "Stars" appear to have the natural ability to grant wishes, although the type of wishes they can grant is dependent on the age, skill, and experience of a Star. After reaching a certain level of maturity, young Stars will ascend from their birthplace of Starborn Valley to the home of the Stars, Star Haven, high above the clouds. After this rite of passage, Stars can begin granting wishes for those they feel are deserving of such an honor. However, a young Star Kid can only grant smaller, more inconsequential wishes, while the extremely old and powerful Star Spirits can grant much more magnificent wishes with more profound consequences. The combined power of the seven Star Spirits is contained within the Star Rod, an ancient artifact that can grant the wish of anyone who wields it.

Star Rod
The Star Rod is a manifestation of the Star Spirits' power and can conceivably grant any wish possible. The only force strong enough to cancel the effects of the Star Rod is the combined powers of the seven Star Spirits, and even then only when manifested in a power known as the Star Beam. In essence, whoever wields the Star Rod has the same amount of power of all seven Star Spirits combined (although he or she may not necessarily control such power effectively). The Star Rod's power can be amplified by other sources of energy, such as the Power Platform Kammy Koopa designed for Bowser to augment the Star Rod's abilities. The Star Rod is normally located in a special sanctuary in Star Haven, guarded by the seven Star Spirits.

Star Road
Star Haven is likely connected to another celestial region above Mushroom World, the Star Road, which also has the power to grant wishes. The exact relationship between the two locations is unknown, but it is possible they are deeply intertwined. Regardless, the Star Road grants wishes differently than the Stars of Star Heaven. The Star Road grants wishes by transforming these desires into special Wish Stars. When a wish is made down below, it is transformed into a star at the Star Road. If and when the wish is granted, the Wish Star turns into a shooting star and falls from the Star Road down to the surface of the planet, specifically Star Hill. This act is connected to the popular belief "wishing upon a shooting star," although the shooting star actually represents that a wish has been granted. Of course wishes made on a shooting star may become Wish Stars at Star Road, and later turn into shooting stars if they are granted, thus continuing the cycle of wish-making.