The first of them uses the sprite of the Kabutops Fossil found in the Pewter Museum of Science. The second one, on the other hand, is represented by a glitched block. The types of both are not defined; they will use the type of the Pokémon whose data was accessed last, just as they will share the leveling up learnset, base stats, and types of it.
The Kabutops Fossil form appears through the old man glitch if w is the character in the third, fifth, or seventh slot of the player's chosen name.
Both forms appear through the Mew glitch with a Special stat of 182.
Unlike the 'Normal' Missingno., the B6, B7 and B8 variants do not crash the game when encountered.
This glitch Pokémon article is part of Project GlitchDex, a Bulbapedia project that aims to write comprehensive articles on glitches in the Pokémon games.