There are three different door keys in the game. The first one appears in Gloam Valley and it is blue with a square-shaped end in appearance. These Door Keys unlock the locked doors of Gloam Valley.
The second type of Door Key is found on Planet Blobule and as a star-shaped end on it. As usual, these Door Keys unlocked the locked doors of Planet Blobule.
The third and final type of Door Key encountered in the game can be found in The Underwhere and is purple in color with a triangle-shaped end. Harga gives away a Door Key after getting her Diet Book from a D-Man. A Door Key is also given away by a Nimbi named Sunbi after saving him from Skellobits.