yep it could be in the public domain, since Missingno is created by garbage data in Pokemon red and blue so it's make by a computer, therefore it's theoretically uncopyrightable

Of course I'm not a legal expert and all, I maybe wrong since you have todo something to see missingno and it's the Pokemon Compeny we're dealing with, they have a couple few $10000000 in their Standard legal funds alone

but it would be so so so cool if we all could use Missingno as inbetween frames for a living glitch sort of character