I just learned today that the Hearthome City gym has a trainer who owns a Drifloon. When I played Pearl as a kid I answered all the questions correctly and skipped all the trainers which meant I couldn't register Drifloon in my pokedex. I didn't have internet access back then so I didn't know about Drifloon appearing on Fridays. After beating the Elite 4 there was only a single pokemon missing in my Sinnoh dex but I didn't know what it was. This lead to me travelling around the region for just over 2 whole years before I unknowingly bumped into something. I looked down at my screen and it was a pokemon I never saw before. A Drifloon. I cried tears of joy that day and praised the Lord.