For some reason I've never picture Missingno to be a bird...
*does not evolve since it's a legendary
A master of disguise. It's true form is not known to humans. It appears to as an odd glitched box with the Water/Bird type to those who are lucky enough. It's is advised not to go near it for it will mess permanently mess up all technological appliances you have on hand. (And in a world like our today that relies heavily on technology imagine how devastating hat would be)