When I was a kid, my friend showed me his collection of legendary pokemon on his Crystal version. He had Mewtwo, Mew, Lugia, Ho-oh, Entei, Raikou, Suicune, Celebei, and all the legendary birds. I was so jealous. He told me I could trade them to my game so that I can have it recorded in my pokedex as long as I traded them back. I'm not proud of this but I never traded them back and he never noticed 😭