One of the PokeIcon sprites for MISSINGNO. when viewed in your party and the only one the doesn't looked glitched or like an actual trainer. [as seen here sta.sh/020b73mc8da ] In fact, this one almost looks like is could be a real thing used in the game normally. And it kinda looks like a stingray. It knows Water Gun and Sky Attack, it is a Bird type, which is the Beta name for the Flying type... Mantine, is that you?
Nuh, I know that MISSINGNO. is just a placeholder when the game doesn't know what Pokemon you should be encountering. It isn't anything else really.

Soon to be in my wife's Etsy shop, alongside many more. www.etsy.com/shop/KyuteSuits