Theoretically speaking, what do you think Missingno would be like if it appeared in the Pokemon anime? Like, what would its origin story, nature, and powers be like to keep it as close to the game glitch as feasible?

You know how sometimes satellite TV gets all pixellated or cuts out entirely because the weather’s bad?  It would look like that.

Okay, okay, serious answer.  I think the obvious answer is that Missingno has to be an offshoot of the Porygon project, specifically of the technology that allows Porygon – a Pokémon composed entirely of data, of information – to manifest itself as a physical entity.  Missingno can similarly convert data into physical reality… but not always smoothly.  You can’t just plug in the code for the Pac-Man video game and have the character Pac-Man materialise in front of you, fully realised and functional; you need to have a program that was specifically written with this process in mind, like Porygon was.  Any other form of data that goes into Missingno results in a garbled mess of matter and energy.  What we “see” as Missingno’s body is actually Missingno’s best effort to interpret the countless radio waves and other signals that are constantly passing through it.  If you just give Missingno a real, physical object, though, it can break that object down into a workable code with which it can create copies of that object.  At some point shortly after its creation the thing crashed through a natural history museum somewhere, and as a result it “knows” how to create copies of several Pokémon fossils.  It’s also possible to coax Missingno to spit out multiple copies of any small object you want (you can’t do this to living things or most larger objects because of safety features built into the core of the original program).  Getting close enough to Missingno to do this isn’t always safe, though – if it picks up on your brain waves and tries to translate them into energy, the pseudo-physical nonsense it produces in response can often cause serious and lasting amnesia.