Mimic

Height: Around 10 feet (approximately 3 meters)—noticeably larger than standard Mimics.
Skin. It becomes black and incredibly durable: the more the Elder Mimic consumes, the stronger this protective layer becomes. Its face, however, is pale pink—this contrast helps it blend into the darkness indoors, but gives it away in open spaces.
Muzzle and face. Eyes protruding. Nostrils partially hidden by the nasal bone.
Mouth and teeth. The teeth are recessed deeper into the throat. And the gums have transformed into sharp, beak-like cartilage—the creature uses it to scrape flesh from bones. The "smile" itself (a wide arch of teeth) is not an expression of emotion, but simply a peculiarity of the facial structure.
Limbs. Sharp claws appeared.
An interesting nuance about vulnerability: despite the impenetrable black skin, the Elder Mimic's weakest point is the face (eyes, mouth, nose area).