u3d-space-shooter/Assets/Scripts/Enemy.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class Enemy : MonoBehaviour
{
    [SerializeField]
    private float speed = 4.0f;

    void Start()
    {
        
    }

    void Update()
    {
        transform.Translate(Vector3.down * speed * Time.deltaTime);

        if(transform.position.y < -5f)
        {
            float randomX = Random.Range(-8f, 8f);
            transform.position = new Vector3(randomX, 7, 0);
        }
    }

    void OnTriggerEnter2D(Collider2D other)
    {
        Debug.Log("Hit: " + other.transform.name);

        if(other.tag == "Player")
        {
            Player player = other.transform.GetComponent<Player>();
            if(player != null )
            {
                player.Damage();
            }
            Destroy(this.gameObject);
        }
        
        if (other.tag == "Laser")
        {
            Destroy(other.gameObject);
            Destroy(this.gameObject);
        }
    }
}