The Three Sacred Treasures are a set of legendary items in the Kid Icarus series. The treasures have belonged to Angel Land since ancient times and give whoever bears them great magical power. To prevent them from being used for evil, they are protected in Sealed Caskets, which only unlocks when all three are together. In the first two Kid Icarus games, Pit travels through Angel Land to retrieve them. When worn by him, he is referred to as Amazing Pit.
Prior to the original Kid Icarus they were taken away by Medusa during her invasion of the Angel Land and given to her strongest servants for protection. They were however retrieved by Pit during his journey to save Angel Land and when brought together the seal on their caskets was broken. Pit could thus use them in the battle against Medusa.
Kid Icarus: Of Myths and Monsters
In Kid Icarus: Of Myths and Monsters, Pit retrieved the treasures once again to receive the power to protect the land from the coming invasion of the demon Orcos. Curiously Palutena states that Pit does not possess the power to wear them, even though he did in the first game. He is thus sent on a mission to battle his way through Angel Land by himself as a mean of training. Palutena sealed the treasures and sent them to be guarded in the fortresses in case the Orcos attacked while Pit was on his mission, and in part of his training he had to defeat the Fortress Guardians. After having reached the Palace in the Sky and retrieved the Sacred Treasures, Pit was strong enough to use the treasures, just in time to fight the Orcos.
Super Smash Bros. series
In Super Smash Bros. Brawl the Mirror Shield appears as Pit's Down Special move. When used, Pit pulls it out and holds it in front of him allowing him to reflect any projectiles with more power than they originally had. While the other treasures doesn't appear, Palutena's Arrow is likely the Light Arrows misnamed, seeing as there are no other arrows made of light in the games. Moreover, Wings of Pegasus are represented in his special moves as the weaker Wings of Icarus. In Super Smash Bros. for Nintendo 3DS and Wii U, the The Three Sacred Treasures became Pit's Final Smash replacing his old Final Smash Palutena's Army.
The Light Arrows is the strongest weapon in the game and is able to pierce through any enemy that comes in it's path. This allows Pit to hit several enemies using a single arrow, unlike his normal arrows. They have their weaknesses however; just like the normal arrows no more than one arrow can be launched at a time. The Light Arrows must be used in the final battle with Medusa, due to her immense strength, to finally end her regime.
The Mirror Shield is an important artifact during the final showdown in the Palace in the Sky. Not only does it deflect projectiles from the many enemies infesting the palace, it is vital in the battle with Medusa. The mere sight of Medusa's eyes would turn Pit into stone, but the shield allows him to reflect her glance. The Mirror Shield appears in Kid Icarus only.
The Silver Armor strangely replaces the Mirror Shield in Of Myths and Monsters, likely due to Medusa not being the enemy this time, and there thus is no need to reflect her deadly glance. The Silver Armor instead boosts Pit's defense, allowing him to take only half the damage he normally would. Interestingly, Pit's appearance when wearing the Sacred Treasures in the first game suggests that he wears the Silver Armor, but it is never noted in the game.
Wings of Pegasus
The Wings of Pegasus grants the bearer the ability of unlimited flight. It thus allows Pit to travel through the Palace in the Sky for the final confrontation with Medusa, which normally would be inaccessible for any ground bound person.
Kid Icarus: Uprising - Idol Description (Three Sacred Treasures)
"The Arrow of Light, Wings of Pegasus, and Mirror Shield Pit used to defeat Medusa 25 years ago. While Pit needs them for his "first" run through Chapter 9, you can later choose to not equip them by tapping the icon on the chapter banner."