6.1 — Gravity & Jump: The First Flick

Compare against your own file rather than copying it. The walkthrough wrote an if that only touches the cave; this version decides the number for both worlds in one ternary - the same behaviour and a different argument: "the Overworld keeps 0 because I said so" rather than "because I never mentioned it". Both are right; pick the one you can defend.

// ------------------------------------------------------------------
//  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;

// PlayerController.cs - the gravity half, complete. Everything from 1.4 to 5.3
// (input, movement, animation, coins, health) stays exactly as you wrote it;
// the flag and the one line under it are the whole of what is new.
public class PlayerController : MonoBehaviour
{
    [SerializeField] private float moveSpeed = 5f;      // your number from 2.2
    [SerializeField] private bool isPlatformer = false; // which world did I wake up in?

    private Rigidbody2D body;

    void Start()
    {
        body = GetComponent<Rigidbody2D>();             // looked up once, per 2.2

        // Decided once, for both worlds. The Overworld's 0 is written here
        // rather than inherited from the prefab, so the decision is visible
        // to anyone reading this file instead of only to the Inspector.
        body.gravityScale = isPlatformer ? 1f : 0f;
    }

    void Update()
    {
        // ... the input, movement and animation lines from 1.4, 1.6, 2.2 and 5.3 ...
    }
}

Compare against your own file rather than copying it. Two differences are worth naming, and neither is a mistake. First the shape: the walkthrough wrote the push inline inside the key check, and this file gives it a method called Jump() - the same line, with a name you can point at when 6.2 and 6.3 start asking what a jump is allowed to do. Second the gravity line: this file decides the number for both worlds with a ternary where the walkthrough only wrote it for one. Your key, your number and the names of your own methods are yours.

// ------------------------------------------------------------------
//  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;

// PlayerController.cs - gravity for the cave, and one flick upward.
// The gravity half came first; the jump assumes it. Up, apex, down: the
// only line that makes the arc is the force, and gravity does the rest.
public class PlayerController : MonoBehaviour
{
    [SerializeField] private float moveSpeed = 5f;      // your number from 2.2
    [SerializeField] private float jumpForce = 7f;      // how hard the flick is
    [SerializeField] private bool isPlatformer = false; // which world did I wake up in?

    private Rigidbody2D body;

    void Start()
    {
        // Looked up once, never inside Update() - the rule from 2.2.
        body = GetComponent<Rigidbody2D>();

        // Decided once, for both worlds.
        body.gravityScale = isPlatformer ? 1f : 0f;
    }

    void Update()
    {
        // ... input, movement and animation, from 1.4 to 5.3 ...

        if (Input.GetKeyDown(KeyCode.Space))
        {
            Jump();
        }
    }

    // The whole jump. One impulse, and gravity spends it over the next half
    // second - which is why there is nothing here about coming back down.
    private void Jump()
    {
        body.AddForce(Vector2.up * jumpForce, ForceMode2D.Impulse);
    }
}