If encountered with the Mew glitch, with a stat of 191, the game will freeze or crash.
The reason the game may crash is because 's front sprite is defined as 256×256 tiles, which causes it to overflow the sprite decompression buffer; for comparison, a normal Pokémon sprite is no larger than 7×7 tiles. Immediately following that buffer is the working memory for the sound engine; corrupting it causes the sound engine to draw upon invalid sound banks, which usually crashes the game. Even if the game doesn't crash, 's front sprite overwrites enough RAM to render normal gameplay impossible.
's cry in battle is part of the sound of the move Surf and variations of Pikachu's cries; however, in its summary it has the cry of a Rhydon, and when withdrawn or deposited at a PC its cry is a slowed-down version of the melody of Cinnabar Island.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.