Goes faster when moving to monster's transform

As i replied in your other post(s) - you're calling the coroutines once a frame. On top of that, each coroutine is looping, to move the object

What you need to do is something like this:

function RotateTowardsMob() {
        if(target != null &&  Vector3.Distance(target.position, transform.position) >= 0.01){
                var direction : Vector3 = transform.position - target.position;
                transform.rotation = Quaternion.Slerp (transform.rotation, Quaternion.LookRotation(-direction), 0.2* Time.deltaTime);
                transform.eulerAngles = new     Vector3(0, transform.eulerAngles.y, 0);
        }
}

for all of the ones that you're calling each frame