enemy death physics

SO i have my enemys walking around the level. they have a rigid body and a collider. Im going to do it so when he collides with my character during his attack animation he gets knocked away and gradually phases away like the enemys in banjo kazooie.

what i want to know is when i have the oncollide expression how do i make the enemy roll away and fade? how do i tell unity to do the physics of that?

This is the basic script i have for my enemy to wander around.

     public class Wanderingai : MonoBehaviour {
     public float speed = 3.0f;
 public float obstacleRange = 5.0f;
 [SerializeField] private GameObject fireballPrefab;
 private GameObject _fireball;

 private bool _alive;

 void Start() {
     _alive = true;
 }
 
 void Update() {
     if (_alive) {
         transform.Translate(0, 0, speed * Time.deltaTime);
     
     Ray ray = new Ray(transform.position, transform.forward);
     RaycastHit hit;
     if (Physics.SphereCast(ray, 0.75f, out hit)) {
             GameObject hitObject = hit.transform.gameObject;
             if (hitObject.GetComponent<PlayerCharacter>()){
             if (_fireball == null){
                     _fireball = Instantiate(fireballPrefab) as GameObject;
             _fireball.transform.position =
             transform.TransformPoint(Vector3.forward * 1.5f);
             _fireball.transform.rotation = transform.rotation;
                 }
             }
             else if (hit.distance < obstacleRange) {
             float angle = Random.Range(-110, 110);
             transform.Rotate(0, angle, 0);
         }
     }
 }

} public void SetAlive(bool alive) { _alive = alive; } }