Cubes are transparent containers that appear in the Subspace Emissary. There are two varieties of these cubes, both of which are opened when attacked to release items. Cubes can be stood on until broken, which may help in rooms where there are falling platforms.
Turquoise cubes are light in color and appear every time an area is entered. They may contain items, collectibles, healing items, or Stock Balls. This cube will contain the same variety of items each time, but the specific item(s) inside may vary. For example, a turquoise cube may always release shooting items. When it contains healing items, it may have multiple varieties of food (like a Party Ball), two Maxim Tomatoes, or two Heart Containers. The quality of the item(s) depends on the difficulty level, stickers attached to the character, and whether continues have been used while playing.
Orange cubes appear on a level only until broken for the first time. They only contain collectibles, as to increase the Clear %. They typically are tucked away in hidden rooms or alcoves. If there are still orange cubes inside of a stage after it has been cleared, a flag will appear on the level in the world map. For an orange cube to count, it not only has to be broken, but the contents must be collected. If broken but the contents uncollected, the orange cube will respawn if the area is left then revisited.