Tower Defense

So I made a test enemy and a test block for a tower defense mod I want to make. Basically, I want the player to be able to build their own path and place a start and an end block, after which the enemies will spawn. Right now all I need help with is getting the enemy to only walk on the custom path block and making it so that entities can walk through it without getting pushed, but I might ask for more help with this later. If someone has the solution, that would be appreciated!