Alien bot, a modular robot, easy to customize by changing each layer or adding components, 

You can put any controller board that fit inside a square of 82mm x 82mm (3.2 in x 3.2in) or inside a circle of 117mm diameter (4.6in).

You can easily control adding a Bluetooth module.https://create.arduino.cc/proj...

You will need 2 micro metal motors (https://www.pololu.com/category/60/micro-metal-gearmotors),  422mm x 19mm wheels (https://www.pololu.com/product/1090),  custom caster ball can be printed adding a a 3/8" diameter metal ball or buy this one https://www.dfrobot.com/produc... (https://www.pololu.com/product/950),  the top part (plo_v2_shell_03a.stl) is for battery storage, you can put a speaker in the front for talk,  use this 10mm diameter RGB LED (http://www.seeedstudio.com/depot/Grove-Chainable-RGB-LED-p-850.html) or similar for the eye.

If you want to add more functions you can use many kind of sensors to fit in the holes