(Game Boy Color)
The parasite was implanted into the body of Lucia when she was a young child.
After being separated from its host by the captain of an Umbrella submarine, it quickly triggered a second biohazardous outbreak and escaped back to the cruiser. When close to being caught, it used its special morphing ability to disguise itself as Lucia. When the real Lucia proved her legitimacy, the parasite was revealed, and it promptly morphed into the shape of a B.O.W. which Leon; Barry and Lucia had met before.
Its ability to change shape made it a particularly covert enemy, with its known forms including Lucia and the "B.O.W.". Another trick "up-its-sleeves" was its ability to mimic the speech of humans, which it did when passing off as both Sherry and Leon.