Queen Leech

The Resident Evil Zero final boss was a giant humanoid mound of sentient leeches. She had control over all other leeches in the Umbrella Corporation Management Training facility. In her first form, she attacks by hitting, grabbing, or throwing, Rebecca or Billy. After enough damage is given she mutates slightly, giving her more attack power and defense. After enough damage she is rendered unconscious and gives up the silver and gold keys that open the blast doors covering the emergency exit shaft. The queen leech has a second form in which she loses most of her human form to become a massive green creature with multiple tentacles and a massive flower-like organ in her back, which continually secretes acid. In that form, she has two main attacks, in which she rams the player character and spews acid from her flower-like organ. She is also invulnerable to all weapons and can only be killed by opening the four emergency helipad shutters to let in sunlight, whose ultraviolet radiation passes through her cells, burning them with a high degree of proficiency, making her highly unsuitable for general use as a biological weapon. Upon the sunlight consuming her body, she was terminated by Billy Coen.