The 6x6x6 magic cube was first made by Verdes and sold under the name V-Cube 6. It is also sold as the Shengshou 6x6x6.
In play it is most similar to the 4x4x4 Rubiks Revenge, because both are of even size. Whereas cubes of odd size have a centre piece on each face that can be rotated but not moved, cubes of even size have no such centre piece. This introduces several complexities that make even-sized cubes much harder to solve than odd-sized cubes. Indeed the V-Cube 6 is a harder puzzle than the V-Cube 7, just as the Rubiks Revenge is tougher than the Professor’s Cube.
As with the Revenge, solving the V-Cube 6 is usually done by reducing it to a 3x3x3 Rubiks Cube. This is done by solving the 4×4 squares inside each of the six faces, and then solving each set of four edge pieces along an edge (known as a tranche). As with the Rubiks Revenge, this almost — but not quite — reduces the puzzle to a 3x3x3 Rubiks Cube. The difference lies in the face that it is impossible to flip a single edge piece of a Rubiks Cube, but quite possible to flip a tranche of edges. Thus we encounter the same parity errors as when solving the Rubiks Revenge by reduction.
You can see from the above that the V-Cube 6 doesn’t really offer anything new. If you can solve the Rubiks Revenge, you can solve the V-Cube 6. Solving the inner faces and tranches is a little more time-consuming but the principles are the same.
Number of positions
According to Wikipedia, the V-Cube 6 has 157 152 858 401 024 063 281 013 959 519 483 771 508 510 790 313 968 742 344 694 684 829 502 629 887 168 573 442 107 637 760 000 000 000 000 000 000 000 000 possible positions; on the short scale you would call this about 157 septentrigintillion.
Variations and related puzzles
The V-Cube 6 is the 6x6x6 in a long series of magic cube puzzles, ranging from the 2x2x2 Pocket Cube, through the 3x3x3 Rubiks Cube, the 4x4x4 Rubiks Revenge, and beyond. There are also cuboids with a non-cubic aspect; for example the 2x3x4.