PlayerController.cs

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


[System.Serializable]
public class Boundary
{
    public float xMin, xMax, yMin, yMax;
}


public class PlayerController : MonoBehaviour
{
    public float speed;
    public Boundary boundary;

    //Shot type 1 (Green)
    public GameObject shot;
    public Transform shotSpawn;
    public float fireRate;
    private float nextFire;

    //Shot type 2 (Blue)
    public GameObject shot_2;
    public Transform shotSpawn_2;
    public float fireRate_2;
    private float nextFire_2;

    //Shot type 3 (Green Big)
    public GameObject shot_3;
    public Transform shotSpawn_3;
    public float fireRate_3;
    private float nextFire_3;

    public Text score;


    void OnTriggerEnter2D(Collider2D other)
    {


        if (other.tag == "GoldStar")
        {
            HealthScript.healthValue = HealthScript.healthValue + 100;
            ScoreScript.scoreValue += 20;
            speed = speed + 2.5f;
            fireRate_3 = 1.0f;
            fireRate_2 = 1.0f;
            Destroy(other.gameObject);
        }

        if (other.tag == "PowerUp")
        {
            HealthScript.healthValue = HealthScript.healthValue + 100;
            Destroy(other.gameObject);
        }

        if (other.tag == "Shot_UFO")
        {
            HealthScript.healthValue = HealthScript.healthValue - 25;
            Destroy(other.gameObject);
        }

        if (other.tag == "Shot_Boss")
        {
            HealthScript.healthValue = HealthScript.healthValue - 50;
            Destroy(other.gameObject);
        }
        if (other.tag == "PowerUp2")
        {
            HealthScript.healthValue = HealthScript.healthValue + 50;
            Destroy(other.gameObject);
        }

        if (other.tag == "PowerUp3")
        {
            HealthScript.healthValue = HealthScript.healthValue + 25;
            Destroy(other.gameObject);
        }

        if (other.tag == "LightningBolt")
        {
            speed = speed + 2.5f;
            fireRate_3 = fireRate_3 - 2.5f;
            if (fireRate_3 <= 0)
            {
                fireRate_3 = 1;
            }
            Destroy(other.gameObject);
        }
    }


    void Update()
    {
        if (Input.GetKey("space") && Time.time > nextFire)
        {
            nextFire = Time.time + fireRate;
            Instantiate(shot, shotSpawn.position, shotSpawn.rotation);
        }

        if (Input.GetKey("q") && Time.time > nextFire_2)
        {
            nextFire_2 = Time.time + fireRate_2;
            Instantiate(shot_2, shotSpawn_2.position, shotSpawn_2.rotation);
        }

        if (Input.GetKey("e") && Time.time > nextFire_3)
        {
            nextFire_3 = Time.time + fireRate_3;
            Instantiate(shot_3, shotSpawn_3.position, shotSpawn_3.rotation);
        }
    }

    void FixedUpdate()
    {
        float moveHorizontal = Input.GetAxis("Horizontal");
        float moveVertical = Input.GetAxis("Vertical");

        Rigidbody2D rigidbody = GetComponent<Rigidbody2D>();
        rigidbody.velocity = new Vector2(moveHorizontal, moveVertical) * speed;

        rigidbody.position = new Vector2
            (
            Mathf.Clamp(rigidbody.position.x, boundary.xMin, boundary.xMax),
            Mathf.Clamp(rigidbody.position.y, boundary.yMin, boundary.yMax)
            );

    }
    
}