Final Fantasy VI · SNES · 1994 · Impact: Data Loss
Under certain conditions — most famously when it misses — Relm's Sketch command reads from the wrong part of memory, scrambling the inventory, equipment and character data and potentially corrupting the save file.
Final Fantasy VI's Sketch command, used by the young painter Relm, copies an enemy and makes it use one of its attacks. In the original release, a Sketch that missed or targeted something the routine couldn't handle made the game draw the "sketch" from the wrong area of memory. The resulting garbage was written back into RAM, with effects ranging from the comic to the catastrophic: inventories filled with large quantities of rare items, equipment and character names changed, and, if the player then saved, the save file could be left damaged. The bug was fixed in later versions of the game. Speedrunners have since turned it into a tool, using carefully controlled Sketch glitches to manipulate inventory and obtain items far earlier than intended.
Sketch has to find an enemy's graphics and attack data before Relm can copy it. When the command misses, or is aimed at a target the routine was not designed for, it ends up working from the wrong addresses. The data it copies and writes back lands in memory that the game uses for other things, including the inventory and character information.
Because the outcome depends on what happens to be in memory at the time, reported effects varied widely: some players found their bag full of rare items, others saw names and equipment change, and the unlucky ones saved a corrupted game.
The bug was fixed in later versions of Final Fantasy VI, but copies of the original release still contain it. In the speedrunning community it is treated as a tool rather than a hazard: in glitched categories, runners set up the inventory and the battle so that the corrupted write produces specific, useful results.
That dual nature — save-destroying bug for ordinary players, precision instrument for experts — has made Sketch one of the most studied single commands in SNES RPG history.