PREFABS & SPAWNING

Turn game objects into reusable templates and spawn them with code!

Course: Game On (9GAMZA) Lesson: T1 — L10 Time: ~75 min Outcomes: G5-1, G5-2, G5-4

What Are Prefabs?

~10 min

+10 XP

▶

Key Vocabulary

Prefab: A reusable template of a GameObject. Change the prefab = all copies update.
Instance: A copy of a prefab placed in the scene. Each instance can be tweaked individually.
Instantiate: The C# command to create a new copy (instance) of a prefab at runtime.
Spawning: Creating objects during gameplay (e.g. enemies appearing, bullets firing).

1.1

The Problem: Imagine you have 50 coins in your game. You want to change the coin sprite. Without prefabs, you'd edit ALL 50 coins one by one. That's terrible!

1.2

The Solution: Prefabs. A prefab is like a cookie cutter. You design the cookie cutter once, and every cookie comes out the same. Change the cutter = ALL cookies change.

Real-world analogy: A prefab is like a class in a school timetable — every student in the class gets the same schedule, but each student can still have their own lunch preference.

1.3

Create your first prefab:

Open your Unity project from last lesson
Create a new sprite: Right-click in Hierarchy → 2D Object → Sprites → Circle
Rename it "Coin" in the Inspector
Change its colour to yellow (Sprite Renderer → Color)
Scale it to (0.5, 0.5, 1) in Transform

1.4

Turn it into a Prefab: Drag your "Coin" from the Hierarchy into the Project window (Assets folder). The name in the Hierarchy turns blue — that means it's now a prefab instance!

What happened? Unity created a .prefab file in your Assets. The object in the scene is now an instance of that prefab.

1.5

Test the power of prefabs:

Drag the Coin prefab from Project into the Scene 3 more times — you now have 4 coins
Position them at different spots in your level
Now double-click the prefab in the Project window to open Prefab Edit Mode
Change the colour to orange
Click the back arrow at the top of the Hierarchy to exit Prefab Mode
All 4 coins should now be orange! That's the power of prefabs.

✓ Checkpoint: I have a Coin prefab in my Project, and 4 instances in my scene that all match.

Prefab Overrides & Components

~10 min

+10 XP

▶

2.1

Override an instance: Select ONE coin in the scene. Change its colour to red. Notice: only THAT coin changes, not the prefab. This is called an override.

Override = a change that ONLY applies to one instance. The prefab stays the same. You'll see a blue bar next to overridden properties in the Inspector.

2.2

Apply or Revert: With the overridden coin selected, click Overrides → Apply All (at the top of Inspector) to push changes TO the prefab. Or click Revert All to undo your changes and match the prefab again.

Apply = make ALL instances look like this one. Revert = make this instance look like the prefab again.

2.3

Add a Collider to the Prefab: This is key — we need coins to be collectible later!

Double-click the Coin prefab to open Prefab Edit Mode
Click Add Component → Physics 2D → Circle Collider 2D
Tick Is Trigger (we want to detect overlap, not block movement)
Exit Prefab Mode — ALL coins now have a trigger collider!

2.4

Tag the Prefab:

In Prefab Edit Mode, go to the top of Inspector → Tag → Add Tag
Click +, type "Coin", click Save
Go back to the prefab, set its Tag to "Coin"
Exit Prefab Mode — all instances are now tagged!

💡 Pro Tip: Always add components/tags to the PREFAB (via Prefab Edit Mode), not to individual instances. This keeps everything consistent.

✓ Checkpoint: My Coin prefab has a Circle Collider 2D (Is Trigger), and is tagged "Coin".

Collecting Coins with Code

~15 min

+10 XP

▶

3.1

Open your PlayerController script. We'll add coin collection to the player, not the coin. Why? Because the player is the one moving — they trigger the collision.

3.2

Add a score variable at the top of your class (with your other variables):

public int score = 0;

3.3

Add the OnTriggerEnter2D method below your Update method:

void OnTriggerEnter2D(Collider2D other)
{
    if (other.gameObject.CompareTag("Coin"))
    {
        score++;
        Debug.Log("Coins: " + score);
        Destroy(other.gameObject);
    }
}

Line by line:
OnTriggerEnter2D — called when something with Is Trigger enters our collider
CompareTag("Coin") — only react to objects tagged "Coin"
score++ — add 1 to our score (same as score = score + 1)
Debug.Log — print score to Console (we'll add UI later)
Destroy(other.gameObject) — remove the coin from the scene

3.4

Save and Test!

Save your script (Ctrl+S)
Go back to Unity, press Play
Move your player into the coins
Check the Console window — you should see "Coins: 1", "Coins: 2", etc.
The coins should disappear when touched!

⚠ Coins don't disappear? Check: (1) Coin has Circle Collider 2D with Is Trigger ON. (2) Coin is tagged "Coin" (case sensitive!). (3) Player has a Collider2D AND a Rigidbody2D. All three are needed for triggers to work!

✓ Checkpoint: When my player touches a coin, the coin disappears and the score increases in the Console.

Spawning Objects with Code

~25 min

+10 XP

▶

Key Vocabulary

Instantiate(): Creates a new instance of a prefab at a specific position and rotation.
Spawner: A script that creates objects at intervals or on events.
InvokeRepeating: Calls a method repeatedly at a set time interval.
Random.Range: Generates a random number between two values.

4.1

Create a new empty GameObject: Right-click in Hierarchy → Create Empty. Name it "CoinSpawner". Position it above the screen (e.g. Y = 6).

4.2

Create a new script: With CoinSpawner selected, click Add Component → New Script. Name it "Spawner". Double-click to open it.

4.3

Delete the default code and type this complete Spawner script:

using UnityEngine;

public class Spawner : MonoBehaviour
{
    public GameObject prefabToSpawn;
    public float spawnInterval = 2f;
    public float spawnRangeX = 5f;

    void Start()
    {
        InvokeRepeating("SpawnObject", 1f, spawnInterval);
    }

    void SpawnObject()
    {
        float randomX = Random.Range(-spawnRangeX, spawnRangeX);
        Vector3 spawnPos = new Vector3(randomX, transform.position.y, 0);
        Instantiate(prefabToSpawn, spawnPos, Quaternion.identity);
    }
}

Line by line:
prefabToSpawn — drag ANY prefab here in the Inspector
spawnInterval — seconds between each spawn (tune in Inspector!)
spawnRangeX — how far left/right objects can spawn
InvokeRepeating("SpawnObject", 1f, spawnInterval) — start after 1 second, then repeat every spawnInterval seconds
Random.Range(-spawnRangeX, spawnRangeX) — random X position
Instantiate(prefab, position, rotation) — create the object!
Quaternion.identity — no rotation (default orientation)

4.4

Connect the Prefab:

Save the script, go back to Unity
Select the CoinSpawner in the Hierarchy
In the Inspector, you'll see Prefab To Spawn — it says "None"
Drag your Coin prefab from the Project window into that slot
Set Spawn Interval to 2 and Spawn Range X to 7

4.5

Press Play! Coins should rain from the top! Move your player to collect them. Check the Console for your score.

Problem: The coins pile up forever! We'll fix this by adding a destroy timer. See step 4.6.

4.6

Auto-destroy spawned objects: Open your Spawner script and change the Instantiate line:

void SpawnObject()
{
    float randomX = Random.Range(-spawnRangeX, spawnRangeX);
    Vector3 spawnPos = new Vector3(randomX, transform.position.y, 0);
    GameObject spawned = Instantiate(prefabToSpawn, spawnPos, Quaternion.identity);
    Destroy(spawned, 5f); // Destroy after 5 seconds if not collected
}

Destroy(object, delay) — the second parameter is the delay in seconds. After 5 seconds, uncollected coins vanish automatically. This prevents memory issues!

4.7

Create an Enemy Prefab: Now make a second prefab!

Create a new sprite: 2D Object → Sprites → Square
Name it "Enemy", colour it red
Add Box Collider 2D (Is Trigger ON)
Add Tag: "Enemy"
Drag to Project to make it a prefab
Delete the scene instance (we'll spawn it instead)

4.8

Create a second Spawner:

Right-click in Hierarchy → Create Empty → name "EnemySpawner"
Add the Spawner script (same script, reused!)
Drag the Enemy prefab into Prefab To Spawn
Set interval to 3 (slower than coins)

4.9

Handle enemy collision: In your PlayerController, add inside OnTriggerEnter2D:

void OnTriggerEnter2D(Collider2D other)
{
    if (other.gameObject.CompareTag("Coin"))
    {
        score++;
        Debug.Log("Coins: " + score);
        Destroy(other.gameObject);
    }

    if (other.gameObject.CompareTag("Enemy"))
    {
        lives--;
        Debug.Log("Lives: " + lives);
        Destroy(other.gameObject);
        if (lives <= 0)
        {
            Debug.Log("GAME OVER!");
        }
    }
}

Make sure you have public int lives = 3; declared at the top with your other variables!

✓ Checkpoint: Coins spawn and can be collected. Enemies spawn and damage the player. Score and lives show in Console.

Extension Challenges

~15 min

+10 XP

▶

🏆 Challenge 1: Moving Enemies — Create a new script called "MoveDown". In Update, add: transform.Translate(Vector3.down * speed * Time.deltaTime); with a public float speed = 3f. Attach it to your Enemy prefab. Now enemies fall toward the player!

🏆 Challenge 2: Power-Up Prefab — Create a green circle prefab tagged "PowerUp". When collected, set a bool isShielded = true and ignore enemy damage for 5 seconds. Use Invoke("RemoveShield", 5f) to turn it off.

🏆 Challenge 3: Difficulty Scaling — Add a variable public float difficultyMultiplier = 0.95f; to the Spawner. After each spawn, multiply spawnInterval by difficultyMultiplier. The game gets faster over time! Use CancelInvoke(); InvokeRepeating(...); to restart with new interval.

🏆 Challenge 4: Object Pooling — Research "Object Pooling" in Unity. Instead of Instantiate/Destroy (which is slow), pre-create objects and reuse them. This is how real games handle hundreds of bullets!

🚀 Boss Challenge: Create a spawner that spawns a MIX of coins, enemies, and power-ups at random. Coins = +1 score, Enemies = -1 life, Power-ups = +1 life. Make a complete mini-game!

PREFABS & SPAWNING

Key Vocabulary

Key Vocabulary

Submission Guide

Quick Reference

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