Shadow Bugs are the small, glowing, violet spheres of which the members of the Subspace Army are made. They are apparently embodiments of a primordial substance. Shadow Bugs were created by extracting a mysterious substance from Mr. Game & Watch, leading Tabuu to have him captured to become the source of the Subspace Army's soldiers. It's hypothesized that Shadow Bugs create the props that Mr. Game & Watch uses in all his attacks, unlike other characters who seem to pull objects from hammerspace.
They first appeared in a Super Smash Bros. DOJO!! update called "This World", which introduced the main plot of the Subspace Emissary. They were shown being dropped down from the Halberd, as well as surrounding a single Primid. The Shadow Bugs are later mentioned in Super Smash Bros for the WII U in Pit's secret taunt while in Pautena's Temple fighting Mr. Game and Watch.
Shadow Bugs are capable of copying a character's trophy and assuming his/her appearance, but are also capable of altering certain qualities such as size, as seen in the fight with the giant Diddy Kong. A copy of a character created by Shadow Bugs will have a purple tinge, be surrounded by a smoky shadow aura, and possess glowing yellow eyes. Bowser himself had a platoon of Shadow Bugs which he ordered to serve as a clone of himself, both to act as a decoy and a second-in-command. Throughout the Subspace Emissary Bowser's Shadow Bugs took on the forms of Peach and Zelda, (whichever princess was rescued) Diddy Kong, Samus, Mr. Game & Watch, and Bowser himself.
Embodiments of a primordial substance that can take the form of any number of lesser Subspace foes. They can also copy the forms of trophies to create evil doppelganger versions of them. The mysterious substance inside Mr. Game & Watch can be extracted endlessly. Once Tabuu discovered this, he used Mr. Game & Watch to create the Subspace Army.
- Despite Bowser having a Shadow clone, he has not been trophied before it is first seen.
- The trophy information of Shadow Bugs is not entirely accurate, as they form Duon on the Halberd, Duon being of an apparently high rank, as it is a late-game boss in the story.
- It is shown that while Shadow Bugs can assume the forms of virtually any organic matter, they apparently can not assume the shape and behavior of more industrial items, such as cannons or bombs.
- It is unknown how Shadow Bugs are extracted from Mr. Game and Watch.
- Shadow Bugs are mentioned in Palutena's Guidance for Mr. Game & Watch, in which Pit says, "Hey, it's a Shadow Bug!". This is a reference to how Shadow Bugs were extracted from Mr. Game & Watch.