Those who create art are sharing a message, and many artists are able to do this in only a few dimensions. Those who use two dimensions must add depth to the length and width by referencing a perspective point, and some of them have the ability to use several. There are also artists who choose three dimensional art forms as their venue, and they have height as well as width and length. If they have a piece that adds diagonals, they might also be considered to create in extra dimensions.
Motion is not often a part of art, so it could be considered an extra dimension. Many pieces give the illusion of motions without ever moving, but they are still restricted to the original dimensions of the piece. A painting that shows motion with blurry lines gives an impression without the use of other space.
Incorporating true motion into a work of art is not impossible, and mobiles are one form where it exists. The artist creates their pieces, and they join them together in a way that allows them to move through space. They then have the potential to move. Some mobiles need an outside force such as the wind to create their movement, and others rely on an attached motor. It does not matter how the movement is created; it is the fact that the piece has moving parts that signifies it is extra-dimensional.
There are no hard rules when it comes to creating art with extra dimensions, and the artist is free to use whatever methods they prefer. Creating pieces with actual motion is more difficult, so many simply create the illusion. Those who do add extra dimensions to their pieces have decided their message needs more reinforcement, or they might simply believe this is the only way to tell their story.