Ah, yes. The ever questioning bird; Missingo. That's what Missingo is, a bird. Infact, Missingo was the Pokémon that Ash saw in the very first episode of Pokémon. Now, I know what you're thinking; "No it's not! That was Ho-oh!". Yeah, you're right. In the first games(red and blue), there is an old cheat to capture Missingo who appears as a mass of dots, nothing more than a glitch. However, that mass of dots was actually Ho-oh, named Missingo. You see, the name is 'Missingo' because he was 'missing'. Get it? I know this sounds opinionitive but it's true and factual. Missingo, even as a mass of dots, can learn Fly. The Gold version of Pokémon will always refer to him as Ho-oh. Missingo is the original name for the missing Pokémon, so I'll always call him Missingo. He's one of my favorites which is why I bought Gold, not Silver.
One more conflict around Missingo is spelling. Some spell it like me; Missingo. Others spell it; Misinggo. Still others spell it; Missingno.