It could take 2,000 hours to unlock this hidden feature in Pokemon Platinum, HeartGold, and SoulSilver, but at least Professor Oak might tell you you're doing a good job

gamesradar.com:

I've spent more hours in the fourth generation Pokemon games than any other game I've ever played, but I can safely say that I've never seen this obscure post-game feature, nor do I think I ever will. 

In Pokemon Platinum, HeartGold and SoulSilver, trainers aspiring to be the very best can take on the Battle Frontier in the post-game, which is full of different facilities to test out your battling skills. One of these facilities is the Battle Hall, which challenges you to build up a win streak using the same species of Pokemon repeatedly, to see how long you can keep winning with just a Pikachu, for example. However, as well as earning Battle Points for prizes, building up a win streak here also earns you fans, including special visitors. 

As explained in this video from YouTube content creator Etchy, details on these visitors have been light on the ground since the games' respective releases, seemingly because the devs made getting them so difficult. There's a nice array of characters who can show up, including your character's mom, rival, gym leaders like Whitney and Jasmine, and even Professor Oak himself. However, the problem is that unlocking them requires a win streak of at least 500 in Platinum, and 1,000 in HGSS, and all three games demand a streak of 10,000 for the rarest ones. That's a lot, even for the most seasoned players.

Thankfully, you don't have to hold one consistent 10,000 win streak to achieve this, as Etchy discovered that your streak number actually adds together your best streaks from each individual Pokemon you've fought with. With that in mind, you could aim for smaller streaks by using everything in the Pokedex. Even so, Etchy calculates that after training everything up and actually participating in the staggering amount of battles required, you could expect the whole process to take up to 2,000 hours. 

But what do these esteemed visitors bring with them after all that effort? Surely, it'd have to be something good, right? Well, not