The Custom Pony game isn't really an actual game, just a simple create your own pony tool using images ripped directly from the Hub's pony flash game.
The game is very easy to use, Pressing the arrows will scroll through the many different features of the pony you are creating, the R resets the feature to it's default, and the ? sets it to a random feature. You can also change the pony's pose between one of many, each pose is fully animated. The picture of the camera on the top right of the screen, when clicked, freezes the pony in place, allowing you to take a smooth and clear screenshot. The R at the top right of the screen sets every feature to something random, creating a fully random pony.
The idea behind the game is practical and simple, but there are a few things that are holding it back. The colors are the major issue, there is a very small range of bright colors you can make your pony, and the other big problem is that it only supports female ponies, which is understandable.