In normal gameplay, Ghost Kirby is only able to possess destructible regular enemies, with all others being unaffected. Despite this, the game contains code for possessing most of the game's mid-bosses (barring Storo and Doc) as well as Gordos, Shotzos, and Squeakers.

The game's data contains an unused red version of the Squeaker enemy, which acts as a more mobile variant of the green Squeaker. These red Squeakers are present not only in isolation, but also in some of the game's similarly inaccessible debug rooms. Given that they are fully coded and that red Squeakers are only normally visible in the Squeak Squad's introductory cutscene and in the Smash Ride sub-game, this implies that they were removed from the main game's levels relatively late into development.

The game contains an unused ability, "Block". It appears to be similar to the Triple Star ability, and is entirely functional beyond being intentionally disabled by making Kirby immediately lose the ability.

In stage 8-3, the slope you encounter in the second room in the Japanese version is a little glitchy. If the player decides to walk and subsequent crouch on the slope, this could possibly put you behind the slope into the out-of-bounds area. This slope happens to be the only occurrence in the game to do this. Crouch-sliding into a wall can make Kirby partially enter said wall. This glitch was fixed in the International version by making the slope completely solid so you couldn't interact into the out-of-bounds area.

In the overworld map of World 7, a shadowy figure can be seen, once the player reaches the area, it is clear that the figure is the Halberd, Meta Knight's airship. It is thought to be the same Halberd that crashed into the ocean at the end of Meta Knight's Revenge in Kirby Super Star.

Kirby had eyebrows added to him on the game's International box art to make him look angry.

In the original Japanese version of Kirby: Squeak Squad, Spinni is referred to as female, but no mention of the character's gender is made in the game's English version, possibly to avoid any controversy with gender issues. However, the American version of Kirby Mass Attack refers to Spinni as male.

When the game was localized in Europe, its name was changed to Kirby: Mouse Attack.

The Design for King Dedede's Castle from the "Kirby: Right Back at Ya!" anime is reused in Kirby: Squeak Squad, Kirby's Epic Yarn & Kirby: Mass Attack, with Squeak Squad featuring the Monster Machine from the anime in the throne room.