The Mirror Cube, aka the Bump Cube is a derivative of the original Rubik's Cube. While having the exact same mechanism, the Rubik's Cube parts all have the same size but differ from one another with the help of colorful stickers, the Mirror Cube is the exact opposite. All of the Mirror Cube's stickers have the same color (traditionally reflective silver or gold - thus its "mirror" like look) but can be difrenciated by size. Each of the Mirror Cube's parts has a different size.
The Mirror Cube was invented in 2006 by Hidetoshi Takeji who at the time called it the "Bump Cube" - The reason for picking that name is the fact that when the puzzle is scrambled it has many "bumps", some parts are larger then the others and stick out.
Solving the Mirror Cube is exactly the same as solving the Rubik's Cube, however it is harder to identify each part because the size difference between the puzzle's parts is less obvious than the color difference of the original puzzle's stickers. The current world record for solving the Mirror Cube is 20.93 seconds and it was set by Wataru Hashimura. The Mirror Cube solving competitions are not WCA offical events.