Hi, i dint know how to reach you in coursera to answer your question, so i hope u can see it here.
Once again good job on the game.
As for the question you asked me in my work, i simply created a script that translates the Foreground Damaging game object in the Y axis at a constant speed.
the script is very simple, in the update function i have this line
this.gameObject.transform.Translate(new Vector3(0, 0.5f*Time.deltaTime, 0));
this ensures the object this script is attached moves in the Y axis at a constant speed, i was also gonna speed it up via triggers as the games went on, but didnt had the time.
Hope this answers your question