@Mixeli

Hi! I hope everything is going well for you! This video serves as a celebration of my 500k subscribers.
Although I haven't yet had a chance to celebrate 300k and 400k, I think it's too late. 
In order to make up for it, I might create a composition to honor them.
I am thankful for all the support I have received in the past month.
It's possible that I am not worthy of the recent subscribers. However, the amount of people who have watched my videos over the years has been honestly astonishing. 
Thank you for giving me the chance to live with my passions.
Reaching a million subscribers isn't my priority at this point. It may be too early. I'm fine with having additional subscribers on my channel to reach this milestone.

Let's go back to my video: this is the complete list of Hidden Bosses found in all Pokémon games up until now. It's possible that some of them are questionable.
It's probable that people have a lot of questions about why some people are considered 'hidden'. If any such questions arise, I will answer them for you.
The video is 6 hours long, and I was very careful and checked everyone carefully. It is truly all hidden bosses in games. 
I produced this video seven years ago. The sequence began with Red and Blue and concluded with Ultra Sun and Ultra Moon (the final games at that time). 
All battles (Appart from Oak) have been completely refurbished with improved quality and resolution this time. The battles are more effective than before. I had a good time while doing it. Remaking those battles took me a minimum of 2 days. After that, I'll have roughly two more days to work on the video.
Enjoy to the fullest!~

@dragonphoenix790

6 hours must be the longest evolution of the Final Bosses, holy sheesh! Congratulations on reaching 500k subscribers!

@shelteringmars391

Fabulous video, Mixeli! I’ll never get tired of the 1st gen “Thunder” animation and sound. It’s just beautiful, very beautiful.

@shelteringmars391

At 6:26, look and that gorgeous Arcanine sprite from Yellow. Absolutely beautiful. It always remembers me Blaine’s gym battle in Yellow: his level 54 Arcanine with “Take Down” and the mighty “Fire Blast”.

@roxasdeviluke317

I remember the days when I'd see pictures of the prof oak fight and he'd  have like 20 pokemon

@hedgehogpower194

I honestly don't think the Scarlet and Violet professors count as secret boss fight as it's part of the main story and the game kinda forces you to play the last story

@TheSandwhichman108

Professor oak ain’t screwing around he leads with a damn Tauros right off the bat!
G1 Tauros was absolutely terrifying.

@jgoincomedy5837

fighting Red when he doesn't say a word is the definition of "on sight".

@kiwishooketh7423

2:23:57 i was just looking around the houses and didn't expect cynthia to be there. I lost to her and never went back in that house

@TheGss4life

I remember the first time I fought when I was a kid. The moment I saw the lvl 80 Pikachu I knew I was cooked.... 😂

@WesleyAPEX

Professor Oak’s theme was so badass

@kylebrandon4556

This must have taken you a really long time to complete. Thank you for this. I hope you continue making great content

@koraldavis3474

I can't wait to see what happens next year for the new Pokémon Z-A game

@wayne0210

I know the music for the prof oak fight is fan made but it's so well done

@Grovyle90

Red in HGSS has a level 88 Pika. The only trainer with a mon to match that level is Cynthia in BDSP. Notice how GF seems very careful not to level npc trainer Pokemon past level 87 in every game thereafter, almost seemingly deliberately so. 

It's almost as if they know who, canonically, is supposed to be the strongest battler.

@NathanTheGameGuy

500K subscribers is quiet a milestone (although now you over 700K at the moment). Congrats!

@zexian9750

I love the silence the moment the gsc protagonist talks to red. It eeriely signifies to the player
"This shouldn't be possible"
"Why is he here?"
"If he's here..."
"....who am I?"
He is here because your goals are of one and the same, after all He was you

@lls2p130

Blue its cool, Red its legendary, Cynthia has some tight bars but Volo, damn that's the real definition of a fucking Deathmatch

@NewplayerXL

A lvl 68 arcanine having to use ember is peak gen 1

@MicaelAlighieri

Several of the bosses here are either unused in the final games or aren't even secret at all, like Professor Oak, Wally and Barry, for example...