There are actually other varieties of missingno, none of which even RESEMBLE a bird. They are:
1. Mr. Pixel Dude (You all know this one)
2. GHOST (Looks like an un-silphed ghost)
3. KABUTO SKELLY (The skeleton of Kabuto...er...a fossil)
4. AERODACTYL SKELLY
P.S.: If you like Mewtwo, choose a name with a "D" in the 3rd 5th or 7th spot on your name. (Example: dxdydxdyd)
When you do the missingno cheat (with the old man and surfing on cinnibar), youll get Mewtwo there (At lvls OVER 100).