No. 204 Hide-and-Seek Monster. It hides in walls and secretly eats the 'seeker.' While it looks like a citizen version of Mecha Chameleon, it has antennae, and its true form features numerous mouths and eyes. Its running form when chased by Merong White and Merong Black perfectly matches Mecha Chameleon. Seeing its arms stretch when attacking Black, it appears capable of extending its body parts. As mentioned, there is no specific data, so standard ammo is sufficient, but seeing it push both White and Black off at once suggests it has high strength despite weak defense. Unlike Mecha Chameleon, which draws itself to hide, this monster has the ability to blend directly into surrounding walls like a real chameleon. According to the music video and the Monster Encyclopedia, it appears in famous places like Mecha Chameleon; if a human (Yaya race) who enters that space fails to find it, it immediately eats them and uses their shadow to multiply and hunt more humans.

Gender: Male. Race: Yaya (Cat). Occupation: Hunter. Relationship: Best friend or brother to Merong White; friend to Spooky, Violet, and Yako; close older brother figure to Sadong. One of the two main protagonists of the Monster Encyclopedia series in Red Long-Johns Yako. He is tasked with recovering monsters appearing on the Yaya planet and delivering them to the research lab. He is Merong White's partner, but they have opposite characteristics. Notably, Black's eyes have minus sign (-) pupils, while White's have plus sign (+) pupils. Black keeps a tidy desk and often engages in negative thinking, whereas White has a messy desk and tends toward positive thinking. When dealing with monsters, Black fights directly with a weapon resembling a handgun, while White uses his head to find clues to resolve the situation without a weapon. White is also primarily responsible for administering vaccine shots to the monsters.

Gender: Male. Race: Yaya (Cat). Relationship: Best friend or brother to Merong Black; friend to Spooky, Violet, and Yako; close older brother figure to Sadong. One of the two main protagonists of the Monster Encyclopedia series in Red Long-Johns Yako. He is tasked with recovering monsters appearing on the Yaya planet and delivering them to the research lab. He is Merong Black's partner, but they have opposite characteristics. Notably, White's eyes have plus sign (+) pupils, while Black's have minus sign (-) pupils. Additionally, White has a messy desk and tends toward positive thinking, whereas Black keeps a tidy desk and often engages in negative thinking. When dealing with monsters, Black fights directly with a weapon resembling a handgun, while White uses his head to find clues to resolve the situation without a weapon. White is also primarily responsible for administering vaccine shots to the monsters.

Gender: Female. Race: Yaya (Cat). Occupation: Hunter. Relationship: Friend to Merong White, Merong Black, Spooky, and Violet. She has multiplication sign (×) pupils. Like the Black and White duo, she appears in yellow, the complementary color to Violet.