How to make transition between scenes in Unity 2D?

Question

Unity

Good afternoon!
I am very interested in the question of how to make a transition between scenes, but at the same time, so that the result obtained in the game was previously saved during the transition.
I myself know how to write a script responsible for the transition between scenes, I'm interested in exactly how to save the points received, or items during the transition.
I also encountered the problem that when switching from 1 to 2 scenes, a large number of times, my clones begin to appear.
I will be glad if you help me with this problem.

Answer 1

Save: 1. https://www.youtube.com/watch?v=oZ1gmpnQBFg (all methods)
2. https://www.youtube.com/watch?v=5NXHO5zjWog&ab_cha... (PlayerPrefs)
Clones: use a singleton ( https://www.youtube.com/watch?v=b91jSnBmVKg&ab_cha... ).