I beat (most of) Pokémon Red using only glitched Pokémon. It was the weirdest playthrough I've ever had in a Pokémon game.
And by glitch Pokémon, I mean Pokemon that are literally glitches, not real Pokémon that can be obtained by glitches. You can see the full Gen I list here.
On one hand, it's kind of absurd that there are over 60 glitch Pokémon in Gen I. On the other hand, the Gen I games are obviously notorious for being profoundly broken, so I guess it shouldn't be surprising that no other generation has anywhere near this number of glitch Pokémon.
Most of these Pokémon are unobtainable or will crash the game, unfortunately. I managed to find six Pokémon that are usable in battle, although there are at least a few more that can be used as well, if I'm understanding correctly.
The team I used had a wide range of stats. The worst one I used was probably "▶ A", as seen here. Exceptional Speed stat, but garbage at everything else. Meanwhile, the MVP of the team was "ゥ .4", as seen here. Just an obscene amount of HP and Defense, with solid Attack and Speed to boot.
I played the game as normal for the first three gyms, and then, right before Erika, I started utilizing the Old Man, MissingNo., Ditto, and Mew glitches to assemble the party. Along the way, I ran into issues with multiple Pokémon and didn't think they were usable, only to figure out what went wrong and solve it, thankfully.
After I did this playthrough, someone told me it's possible to go out of bounds as soon as Pewter City, and you can obtain glitch Pokémon even earlier. Darn. Now I know for next time I guess.
ALT TEXT: This post features a collection of seven different images, most of which are screenshots from Pokémon Red itself. The first image features Gym Leader Erika's sprite after being defeated, which has been rearranged into several pieces and made to be out of order, likely due to the usage of the glitch Pokémon MissingNo. The second image shows glitch Pokémon "M", which has the typing "Bird" and Normal. The third image shows the evolution tree for glitch Pokémon "M", with two different paths possible. The first path shows that it will evolve into Kangaskhan if given a Rare Candy at Level 0. The second path shows that it will evolve into Clefairy at Level 128 if given a Rare Candy, and then Clefairy evolves into Clefable with a Moon Stone (as it normally does). The fourth image is a screenshot of a Bulbapedia page, showing the importance of catching a Magneton before attempting to catch the glitch Pokémon called "ゥ .4". Otherwise, upon capture of "ゥ .4", the game will open its Pokédex entry and play a chaotic glitch song that never ends, which prevents the player from proceeding further in the game. The fifth image shows the typing for glitch Pokémon "ゥ .4", which is "PokéManiac". The sixth image shows the moveset that glitch Pokémon currently knows, including "TM28" and "N". The seventh and final image shows the fully assembled glitch Pokémon team from the party screen, some of which have random NPC sprites instead of Pokémon sprites. To the side of this is Patrick Star from the TV show SpongeBob SquarePants, holding an ice cream cone and yelling "Who are you people?!"