Replace a character with a ragdoll or wreck

In a game you might want to switch an asset such as a character, vehicle, or building from an intact state to a destroyed state. Rather than modifying the intact version of the GameObject (by removing scripts, adding Rigidbody components and so on), it’s often more efficient and effective to delete the intact GameObject and replace it with an instantiated destroyed prefab.

This gives you a lot of flexibility. You could use a different Material for the destroyed version, attach completely different scriptsA piece of code that allows you to create your own Components, trigger game events, modify Component properties over time and respond to user input in any way you like. More info
See in Glossary, or instantiate a prefab containing the GameObject broken into many pieces to represent a wrecked or shattered state. Any of these options can be achieved with a single call to Instantiate, to bring your destroyed version into the SceneA Scene contains the environments and menus of your game. Think of each unique Scene file as a unique level. In each Scene, you place your environments, obstacles, and decorations, essentially designing and building your game in pieces. More info
See in Glossary, while deleting the original.

Most importantly, you can create the destroyed version which you Instantiate with completely different GameObjects compared to the original. For example, to create a breakable robot, you would model two versions: one that consists of a single GameObject with MeshThe main graphics primitive of Unity. Meshes make up a large part of your 3D worlds. Unity supports triangulated or Quadrangulated polygon meshes. Nurbs, Nurms, Subdiv surfaces must be converted to polygons. More info
See in Glossary Renderer and scripts for robot movement, and the other that consists of several skeletal parts that can be controlled individually by physics.

Your game runs faster when using the model with just one GameObject, because the model contains fewer triangles and so it renders faster than the robot that has many small parts. Also while your robot is happily walking around, there is no reason to have it in separate parts.

Build a wrecked robot prefab without code

To build a wrecked robot prefab without code:

1. Model your robot with lots of different skeletal parts in your favorite 3D modeling software, and export it into the Assets folder of your Unity Project.

2. Create an empty Scene in the Unity Editor.

3. Drag the model from the Project window into the empty Scene.

4. Add Rigidbodies to all parts, by selecting all the parts and choosing Component > Physics > Rigidbody.

5. Add Colliders to all parts by selecting all the parts and choosing Component > Physics > Mesh Collider (enable the Convex option for faster performance).

6. Make sure you parent all the parts of your wrecked robot to a single root GameObject.

7. For an extra special effect, add a smoke-like Particle SystemA component that simulates fluid entities such as liquids, clouds and flames by generating and animating large numbers of small 2D images in the scene. More info
   See in Glossary as a child GameObject to each of the parts.

8. Now you have a robot with multiple explodable parts. The parts can fall to the ground because they are controlled by physics, and each part creates a Particle trail due to the attached Particle System.

9. Click Play to preview how your model reacts, and make any necessary tweaks.

10. Drag the root GameObject into the Assets folder in the Project window to create a new Prefab.

Build a wrecked robot prefab from code

The following example shows how you can model these steps in code:

using UnityEngine;
public class WreckOnCollision : MonoBehaviour
{
   public GameObject wreckedVersion;

   void OnCollisionEnter()
   {
       Destroy(gameObject);
       Instantiate(wreckedVersion,transform.position,transform.rotation);
   }
}

You can download a Project containing all these example, here: InstantiatingPrefabsExamples.zip

Additional resources

• PrefabsAn asset type that allows you to store a GameObject complete with components and properties. The prefab acts as a template from which you can create new object instances in the scene. More info
  See in Glossary
• GameObjectThe fundamental object in Unity scenes, which can represent characters, props, scenery, cameras, waypoints, and more. A GameObject’s functionality is defined by the Components attached to it. More info
  See in Glossary