Minecart like entity

I want to make a mob where it walks only on a specific block and cannot go out of that kind of block and make it continously walk and cannot go backwards... I am first thinking about to make it a minecart like entity that just walks forward and only on rails but idk how to do that so pls reply with either about creating a minecart like entity (with rails) or have a different idea to make my mob like that... pls reply even if you don't know the answer because that would just let me know people actually see this.