Dark Cube (from the indie-game "Edge") is dark greyish to black colored square and the only object that has a move pattern like the player.
Dark Cube only appears in the 'Extended Levels'. He is encountered 6 times by the player (in the levels: 6, 16, 23, 28, 34, 41). Noticeable is, that every time you face him, the platforms have a dark color (the first and last confrontation in the levels 6 and 41 have white platforms). His main actions are based on moving/ fleeing to buttons which let platforms move and/ or disappear.
Dark Cube shares the same move pattern like the player and so is able to move free (out of his own accord). He can hold himself a long time at another cube or climb up one cube high. His moves are slow and careful but in certain parts he even moved way faster than the player ever could. It is unknown, why Dark Cube wants to get rid of the player or even, if he knows what he does (the final level makes it look like, that he really wants to defeat the player and make him fall into the endless pits). His actions make him mainly an antagonist but some of his actions help the player to reach the goal (beginning of level 6) and make him to some kind of anti-hero.
If Dark Cube is caught up by the player in another level than the 41. ,he will teleport himself to the next platform. He often waits for the player to get near him and then starts to act by moving and trying to make the way to the goal platform harder. Every time the player is about to end a level, Dark Cube disappears in nowhere.
There are two different ways of meeting him: He moves at an own platform part, or he shares the same platform(s) with you.
Appearance in "Edge"
Level 6 "Dark Cube":
During the first encounter, he helps the player to reach the next platforms by pressing buttons near him. After some seemingly friendly actions hew begins pressing buttons that make platforms underneath the player disappear.
Level 16 "Dark Edge Time":
During this level he only presses buttons that help the player to continue. Certain platforms can become dangerous as they could push the player down into the endless pits.
Level 23 "Deadly Race":
The first level in which the player and Dark Cube move on the same platforms. He moves way faster than before and heads toward the goal. Meanwhile he moves mainly over cubes that shortly fall into the endless pits afterwards, leading to that the player has to find alternative routes.
Level 28 "Wire":
With the help of buttons he brings the 'wire platforms' on the player side into movement.
Level 34 "Robot Sport":
At the beginning of the level, Dark Cube uses the block-robots to grab the platform with the player on it, to bring the player to the next platform. Here he uses his robot to try making you falling down. If the protagonist passes the narrow labyrinth-like way, Dark Cube leaves and is seen later, when the player is on top of one robot. Dark Cube uses a second block-robot to smash the protagonist against a wall, which ends in the defeat of the players block-robot. At the end, Dark Cube uses the block-robot to blockade your way until the player finds one to get to the goal platform.
Level 41 "Final Clash":
During the final level, he uses a second and last time the same platforms as you. He waits directly at the start for the player and moves at the beginning very fast. He presses buttons push you with cube walls down or to block your way. This blockades can be only avoided by moving over the side walls. After this phase he presses buttons which let platforms disappear. If this phase is over, the protagonist has to move very fast over all obstacles in his and Dark Cubes way. At the beginning he will be faster than the player and press every button to make the way behind and under the player disappear to let him fall down and lose.
At the end the player can become faster by showing a lot of skill and using Dark Cubes slowness against him. It is necessary to reach the last button to defeat Dark Cube. If the player is slower, Dark Cube will press it and the player loses. If the button is pressed by the protagonist, the platform behind the button moves away and slowly moves behind a two cube high wall.
Dark Cube tries to hold himself at the wall when the platforms completely disappeared but after 2 seconds he fails and falls down. Some seconds later the doors barraging the goal platform open and let you reach the end. It is unknown what happened after the "Final Clash" to Dark Cube but with all these similarities between the protagonist and him it's possible, that Dark Cube died by falling into nothing/ the unknown.