/vr/ - Retro Games

Absolutely. Tons of shit.

Missingno and 'M weren't the only glitch Pokemon. There are a whole bunch of bizarre specimens that can have different effects on your game. Some are basically junk data, others hint at removed concepts.

http://bulbapedia.bulbagarden.net/wiki/List_of_glitch_Pok%C3%A9mon

Also, glitch trainers. Including "Chief" and "Prof. Oak".
http://bulbapedia.bulbagarden.net/wiki/Glitch_Trainer

Looking at concept art shows a bunch of unused designs and crap, including a really cute female PC that became Green in the manga and Leaf in the games.

http://bulbapedia.bulbagarden.net/wiki/Pok%C3%A9mon_Red_and_Green_beta

There was an unreleased game called Pocket Monsters RPG for the N64DD. Plus, Japan got another Pokemon Stadium that never came to America or Europe.

http://bulbapedia.bulbagarden.net/wiki/Pocket_Monsters_RPG

And there's an unreleased puzzle game.

http://bulbapedia.bulbagarden.net/wiki/Pok%C3%A9mon_Picross

And if we want to go into spinoffs, barely anything about the original "Pocket Monsters" manga is common knowledge.

That mostly covers Gen 1. May be some more Gen 2 stuff. So, yeah. There's some stuff.