HUMPHREY can be interacted with his insides through buds. Each bud seems to be tasked with something by the SLIME GIRLS or just there to fill the emptiness of his gut with mundane activities, such as games and relaxing. He appears to be easygoing and fun-loving, shown especially in MEDUSA's lab by how he has designed games that can be played inside himself. He can also be careless and prone to mistakes, demonstrated mainly in MOLLY's lab. His buds appear to be afraid of MARINA, as she uses them as test subjects.

However, he is easily overwhelmed by his hunger for clams. If he is unable to eat clams, he resorts to eating anything, including the SLIME GIRLS, and even turning on the party to satiate it. He is extremely sadistic, toying with OMORI and his friends and telling them that their struggle is futile. He also has a habit of speaking in rhymes during his boss fight as well. He also contains skeletons in his gut, which are implied to be the remains of past visitors who did not make it out alive.

BRANCH CORAL states that HUMPHREY has lived for so long that he lost his sense of morality, explaining why he was so quick to decide to devour OMORI and friends despite being friendly to them earlier. This implies that HUMPHREY may have been kinder and more empathetic in the past.