Cool rollback toy versions.... Great STEM projects

What can be added to a rollback toy to make it more interesting? How about walking feet , jumping grasshoppers, frogs, kangaroos moonwalking shoes and a rabbit racing against a tortoise. All these examples plus a few more can be added to the side of a rollback toy to make it a fun and challenging STEM activity for young students.
Build instructions can be found here
https://www.youtube.com/watch?v=v3V_8ZRxXGU
Tthis video is being reposted due to copywriter issues on the original post