Bad sprite
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A bad sprite (named after bad clone) is a glitch Pokémon with a sprite that causes memory corruption when it is viewed.
Most commonly in Pokémon Red, Blue, and Yellow the sprite will affect the SRAM and possibly corrupt the Hall of Fame.
A bad sprite that causes a glitch battle is typically due to bad sprite dimensions. A dimension of x0 (apparently it is effectively x256) in width or height will result in the game unpacking a huge sprite. As part of unpacking the sprite, data is temporarily stored in bankless portions of SRAM but it is possible for a buffer overflow when later areas of SRAM are touched (the reason encountering MissingNo. corrupts the Hall of Fame/results in a saving message on Stadium Game Boy Tower etc.). Furthermore, glitch Pokémon sprites of both width 0 and height 0 will typically corrupt the memory even further; exceeding the end of SRAM in the memory map (SRAM ranges from A000-BFFF) and touching C000 and beyond; the beginning of WRAM.
Certain glitch Pokémon including Yellow MissingNo., 4 4 (hex:BF) and 4(h4? (hex:ED) can corrupt the current battle (an effect known as a glitch battle not to be confused with a glitch encounter system) in ways such as corrupting what is on the screen or causing glitch music. Occasionally, they will corrupt bytes in memory that will lead to freezes; such as C0EF/C0EF (the audio ROM bank and the saved copy of it, where the only valid sound banks are 02, 08, 1F, 20 (Yellow only)/28 (Japanese Yellow) and any other sound bank will lead to glitch sound commands which typically freeze the game; though some corruption is possible with bank 20 as well).
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