How to make flips, backflips like in game Backflip madness

You'll need to use rotation scripts.

Personally I was too lazy to write one myself but I used this script as reference for my projects:

 using UnityEngine;
 using System.Collections;
 
 public class testflip : MonoBehaviour {
 
     public float myRotationSpeed = 100.0f;
 
     public bool isRotateX = false;
     public bool isRotateY = false;
     public bool isRotateZ = false;
 
     // CHANGE TO ROTATE IN OPPOSITE DIRECTION
     private bool positiveRotation = false;
 
     private int posOrNeg = 1;
 
     // Use this for initialization
     void Start ()
     {
         //get current rotation
         GetComponent<Collider>().isTrigger = true;
         if(positiveRotation == false)
         {
             posOrNeg = -1;
         }
     }
 
     // Update is called once per frame
     void Update ()
     {
             //  Toggles X Rotation
             if (isRotateX) {
                 transform.Rotate (myRotationSpeed * Time.deltaTime * posOrNeg, 0, 0);//rotates coin on X axis
                 //Debug.Log("You are rotating on the X axis");    
             }
             //  Toggles Y Rotation
             if (isRotateY) {
                 transform.Rotate (0, myRotationSpeed * Time.deltaTime * posOrNeg, 0);//rotates coin on Y axis
                 //Debug.Log("You are rotating on the Y axis");
             }
             //  Toggles Z Rotation
             if (isRotateZ) {
                 transform.Rotate (0, 0, myRotationSpeed * Time.deltaTime * posOrNeg);//rotates coin on Z axis
                 //Debug.Log("You are rotating on the Z axis");
             }
     }
 }

Obviously you'll need to customize that script but it shows how to rotate objects in C#