I want to make a game where you can switch from 2D 8 bit to 3D third person by going through a door. How would I code this?

@dinobert10

What have you tried so far? I played around a bit and at least figured out a hard part for you. The switch from 3d cam to 2d. So here you go:

 using UnityEngine;
 
 [RequireComponent(typeof(Camera))]
 public class CameraProjectionChange : MonoBehaviour
 {
     public float ProjectionChangeTime = 0.5f;
     public bool ChangeProjection = false;
 
     private bool _changing = false;
     private float _currentT = 0.0f;
 
     private void Update()
     {
         if (Input.GetKeyDown(KeyCode.Tab))
         {
             ChangeProjection = !ChangeProjection;
         }
 
         if (_changing)
         {
             ChangeProjection = false;
         }
 
         else if (ChangeProjection)
         {
             _changing = true;
             _currentT = 0.0f;
         }
     }
 
     private void LateUpdate()
     {
         if (!_changing)
         {
             return;
         }
 
         var currentlyOrthographic = GetComponent<Camera>().orthographic;
         Matrix4x4 orthoMat, persMat;
         if (currentlyOrthographic)
         {
             orthoMat = GetComponent<Camera>().projectionMatrix;
 
             GetComponent<Camera>().orthographic = false;
             GetComponent<Camera>().ResetProjectionMatrix();
             persMat = GetComponent<Camera>().projectionMatrix;
         }
         else
         {
             persMat = GetComponent<Camera>().projectionMatrix;
 
             GetComponent<Camera>().orthographic = true;
             GetComponent<Camera>().ResetProjectionMatrix();
             orthoMat = GetComponent<Camera>().projectionMatrix;
         }
         GetComponent<Camera>().orthographic = currentlyOrthographic;
 
         _currentT += (Time.deltaTime / ProjectionChangeTime);
         if (_currentT < 1.0f)
         {
             if (currentlyOrthographic)
             {
                 GetComponent<Camera>().projectionMatrix = MatrixLerp(orthoMat, persMat, _currentT * _currentT);
             }
             else
             {
                 GetComponent<Camera>().projectionMatrix = MatrixLerp(persMat, orthoMat, Mathf.Sqrt(_currentT));
             }
         }
         else
         {
             _changing = false;
             GetComponent<Camera>().orthographic = !currentlyOrthographic;
             GetComponent<Camera>().ResetProjectionMatrix();
         }
     }
 
     private Matrix4x4 MatrixLerp(Matrix4x4 from, Matrix4x4 to, float t)
     {
         t = Mathf.Clamp(t, 0.0f, 1.0f);
         var newMatrix = new Matrix4x4();
         newMatrix.SetRow(0, Vector4.Lerp(from.GetRow(0), to.GetRow(0), t));
         newMatrix.SetRow(1, Vector4.Lerp(from.GetRow(1), to.GetRow(1), t));
         newMatrix.SetRow(2, Vector4.Lerp(from.GetRow(2), to.GetRow(2), t));
         newMatrix.SetRow(3, Vector4.Lerp(from.GetRow(3), to.GetRow(3), t));
         return newMatrix;
     }
 }

After that I need a bit more info because this is a pretty vague question. I would like to know what you have thought up so far and what you are planning to do. It would help me help you more.