If encountered with the Mew glitch, with a stat of 191, the game will freeze and no action can be taken, which then leads to a crash.
The reason the game may crash is because 4 4's front sprite is an unusually large 256x256 pixels, which causes it to overflow from RAM to SRAM and corrupt the current sound bank identifier address to invalid sound banks, and invalid sound banks usually crash. Even if the game doesn't crash, 4 4's front sprite will overwrite enough RAM to otherwise prevent play.
's cry in battle is part of the sound of the move Surf and variations of Pikachu's crys; however in its summary it has the cry of a Rhydon, and when withdrawn or deposited at a PC its cry is a slowed-down version of the melody of Cinnabar Island. 's solid glitch screen makes using it in battle difficult, as the player won't be able to see the battle menu.
As its primary type is one of the glitch types, which do not have any weaknesses or resistances, this glitch Pokémon has the same weaknesses and resistances as a pure Normal-type Pokémon.
According to TheZZAZZGlitch, when the game attempts to decompress 's sprite, it goes so wrong that it tries to read its sprite data from VRAM. VRAM is only accessible for a short time every frame, so the sprite data is filled with random 0xFF bytes. This makes the sprite's appearance essentially random.
This glitch Pokémon article is part of Project GlitchDex, a Bulbapedia project that aims to write comprehensive articles on glitches in the Pokémon games.