2.2 — Spikes: Physics, Damage & Death

Compare against your own file rather than copying it. The gap is the linearVelocity line: there is no deltaTime because velocity is per second, and the frozen rotation exists because solid collisions push.

// ------------------------------------------------------------------
//  REFERENCE FILE — Assets/Scripts/PlayerController.cs
//  Written to be read, not pasted. Build it with the walkthrough
//  above, one step at a time, then open this and compare.
//  If it is sitting in your project unchanged, that is the thing
//  to go and do now — the walkthrough is still above you.
// ------------------------------------------------------------------
using UnityEngine;

public class PlayerController : MonoBehaviour
{
    // ---- class body: every field lives up here, above Start() --------------
    [SerializeField] private float moveSpeed = 5f;
    [SerializeField] private int health = 3;                     // <- new in 2.2
    [SerializeField] private int coins;                          // from 2.1

    private Rigidbody2D body;                                    // <- new in 2.2
    private float inputX;
    private float inputY;
    private Animator animator;                                   // from 1.6
    private SpriteRenderer spriteRenderer;                       // from 1.6

    // ---- methods you own --------------------------------------------------
    void Start()
    {
        body = GetComponent<Rigidbody2D>();                      // <- new in 2.2
        animator = GetComponentInChildren<Animator>();
        spriteRenderer = GetComponentInChildren<SpriteRenderer>();
    }

    void Update()
    {
        inputX = Input.GetAxis("Horizontal");
        inputY = Input.GetAxis("Vertical");

        Vector2 direction = new Vector2(inputX, inputY);
        direction = direction.normalized;

        // No Time.deltaTime: velocity is per second, not per frame.
        body.linearVelocity = direction * moveSpeed;
    }

    void UpdateAnimation()
    {
        // unchanged from 1.6
    }

    // ---- callbacks: Unity calls these, you never do -----------------------
    private void OnCollisionEnter2D(Collision2D collision)
    {
        // Collision2D, not Collider2D — so the tag is asked of .gameObject.
        if (collision.gameObject.CompareTag("Spikes"))
        {
            TakeDamage(1);
        }
    }

    private void OnTriggerEnter2D(Collider2D other)
    {
        if (other.CompareTag("Coin"))
        {
            coins = coins + 1;
            Debug.Log("Coins collected: " + coins);
            Destroy(other.gameObject);
        }
    }

    private void TakeDamage(int amount)
    {
        if (health <= 0)
        {
            return;
        }

        health = health - amount;
        Debug.Log("Health: " + health);

        if (health <= 0)
        {
            Debug.Log("Player died.");
        }
    }
}