Oh yes, the most famous glitch in gaming is still present in the eShop versions of the original Pokémon games. Here’s a step-by-step guide on how to pull it off, in case your memory is rusty.
The easiest way to encounter Missingno is through something called the “old man glitch.” You can’t do this right away; you need to have both A) visited Cinnabar Island and B) know fly. With that in mind, first, you need to talk to a man found in the northern part of Viridian City, a location in Pokémon Red and Blue. He looks like this:
You’ll want to let him teach you how to catch a Pokémon—yes, even if you already know how to do it. After his demonstration, you should fly to Cinnabar Island, another location in Red and Blue. From there, you need to surf on the eastern coast of the island. The trick is that you can’t go off into the water—you have to keep “surfing” on the land touching the water, like so:
While doing this, you might encounter random Pokémon with all sorts of wild levels—but occasionally, you might encounter Missingno. Jackpot! Missingno comes in a few different varieties, such as...
Missingno, as many of you already know, is not a normal monster. It’s literally not supposed to exist, which is also why, once you have it in your party, things can get kind of funky.
Missingno can go over level 100. It can learn certain moves more than once. It can’t evolve. It has the highest attack stat in Red and Blue, but also the lowest defense stat. And, according to Nintendo, it can actively corrupt your game. So, if you do choose to capture it, do be careful!
There’s a benefit to capturing Missingno, of course. Aside from coolness, Bulbapedia states that encountering this monster can duplicate items for the player:
The sixth item in the Bag is duplicated upon encountering the glitch Pokémon, and again if it is caught. The quantity of this item will be increased by 128, provided that the quantity is less than 128 before performing the glitch. This means that the player is free to perform the glitch again by swapping the item, or using/tossing the duplicated item to reduce its quantity back under 128.
If you’d like to see the glitch in action, here’s a video by Epi Demie on the newest version of Pokémon Blue. Note that it’s all in German.
In case you’re curious, no, he has not tried uploading it to Pokémon Bank. I’m not sure it would work, though.