How to create a bouncing in z space

I would make a pre-comp with a ball bouncing up and down (no z-space). Then move that composition in Z space. Then add a separate pre-comp to act as a light-bounce when it gets close to a surface. I made both comps with black backgrounds then set them to screen under the mode. You might want to add a secondary glow. That's what I did in this video to simulate a fireball. 
https://youtu.be/RBMaC_xcbs8?t=37

Here is a better breakdown of the fireball:

https://www.behance.net/gallery/61287711/Mario-VR

There are about a dozen easy ways to simulate a ball of light moving through a scene. 

You can create a pale yellow solid that is about 400 X  400 pixels, double click the ellipse tool to create a circular mask, press mm to reveal mask properties and reduce the size of the mask and increase the feather. Then add your background layer, change the blend mode of the solid to Add and animate position and scale.

You can add a black solid to the timeline, then add Lens Flare, then animate the brightness and the position of the flare center. Then change the blend mode of the Lens Flare layer to Add and put it over a background. 

You could invest in some 3rd party plug-ins like Trapcode Lux, add a light to the scene, and use Lux to make the light source show up in the scene.

You could make the lens flare layer 3D and animate the position.

I could go on and on. I don't know your experience level, or your design goals, or whether or not you are simulating a ball of light in a video. Give us some details, show us an example, embed some screenshots, and maybe we can point you to an efficient solution. Any solution we provide will require some skill in setting keyframes and animating properties like position and intensity. There is no solution that is a one-click trick.

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