Theres a few different forms of how Missingno looked depending on where you did the glitch to spawn him. The first one I sent I think was if you did it on the tiles next to cinnabar island the second & third one I think second was going out of bounds in a cave & third was out of bounds on grass.

Most people know this one which if I remember you got this one if you did it by where the S.S anne takes off.