Fused Shadow

The Fused Shadows are a set of four parts that collectively form a helmet-like mask. Each part is a physical manifestation of the interlopers' dark power. The Fused Shadows make their first and main appearance in The Legend of Zelda: Twilight Princess. Midna wears one of the Fused Shadows as a mask in her imp-like form.

As the Twilight Princess, Midna is the only character who can control the Fused Shadows' dark power, especially as a descendant of the interlopers. Others who come in contact with the Fused Shadows become evil monsters, such as Darbus, who became Fyrus.

The Legend of Zelda: Twilight Princess
In The Legend of Zelda: Twilight Princess, after Link restores light to the Faron Province, Faron appears and tells him to collect the Fused Shadows, which are the only thing powerful enough to destroy Zant. According to Faron, the Fused Shadows were hidden by the goddesses, and only the Spirits of Light know of their locations. Link and Midna go on an adventure to search for the missing three Fused Shadows. The Fused Shadows are located in the Forest Temple, Goron Mines, and the Lakebed Temple respectively, and are guarded by Diababa, Fyrus, and Morpheel respectively.

Later, Lanayru tells Link about the origin of the Fused Shadows through a nightmarish vision. It shows that the Interlopers created the Fused Shadow and attempted to use it to conquer the Sacred Realm. After they were banished to the Twilight Realm, the Fused Shadow broke into four pieces. One of them was sealed within the Twilight Realm and is the piece Midna wears. Shortly after Link and Midna recover the last Fused Shadow, Zant steals the three they have collected at Lanayru Spring. Much later in the game, after Link defeats Zant in battle in the Palace of Twilight, Midna uses the power of the Fused Shadows to kill him, but accidentally completely obliterates him.

When Link and Midna reach Hyrule Castle, she uses the Fused Shadows' power to transform into a giant spider-like form and destroy the castle's surrounding barrier. In the final battle, after Link defeats Ganon, Midna warps Link and Zelda outside of Hyrule Castle. Midna tries using all of the Fused Shadows' power to destroy Ganondorf, although she is outmatched because Ganondorf inherited a stronger power, the Triforce of Power. Ganondorf emerges victorious, holding Midna's Fused Shadow and crushing it.

During the ending credits, a piece of a Fused Shadow is shown partially buried in Hyrule Field.

The Legend of Zelda: Breath of the Wild
In The Legend of Zelda: Breath of the Wild, there is a head armor called Midna's Helmet, which is based on the Fused Shadow. This is affirmed by its in-game description, which says it is "much like" the Fused Shadow.

Hyrule Warriors
In Hyrule Warriors and its reissues, the entire Fused Shadow is used in Midna's Focus Spirit attack, in which she transforms into her tentacled beast form and attacks with a giant spear before resuming her normal form. Midna's discarded Fused Shadow is shown in Twili Midna's battle intro cutscene. Midna's Fused Shadow also appears as both Midna's and Twili Midna's gold Material drop.

In Hyrule Warriors Legends, the Fused Shadow appears as Midna and Dark Midna's Gold Material drop. Twili Midna no longer drops the Fused Shadow, which is replaced by Twili Midna's Robe. The Fused Shadow Mask (which is the complete Fused Shadow) appears as a Fairy Clothing Headgear option for Companion Fairies.

Trivia

 * In Animal Crossing: City Folk, there is a helmet called "Midna's Mask", which is the Fused Shadow along with her hair. It can be obtained for 6,500 points through the Nook's Point-Tracking Machine system.