This was a book I kept revisiting all throughout my childhood. I finished Pokemon Yellow really quickly without its help before I got it, but after I got Red and Blue, it became an invaluable asset.
I added my own notes (like where hidden items are) and it's made each playthrough that much more fun. It's like a relic from my childhood now. Its pages fell apart and it's in terrible condition, but I will never get rid of it. I'd still use it today.