The true villain of the second season, Melvin is Marik's imaginary friend, to "give him all the hugs he ever wanted", created by him as a child to deal with years of abuse and live-action Disney movies. Yami is initially skeptical of Melvin's butting into the show, until Melvin proves himself more evil than Marik by revealing that he was the one who suspended Team Four Star, the creator of Dragonball Z Abridged.
Possibly as an exaggeration of Yami Marik's insanity, Melvin constantly offers to hug people but in truth just wants to stab them (possibly also a joke that in the dub the Millennium Rod's concealed dagger is edited out). In "Requiem For A Nyeh", Melvin claims Marik invented him to deal with his loneliness, as Melvin "would give him all the hugs he'd ever need". Also, no matter what people say, he frequently claims he is controlling a person's mind.
He also has the habit of calling people "Binky-Boy", a habit Marik shared, and otherwise gives people bizarre nicknames, such as "whore-biscuit" for Mai, "chucklenuts" for Ishizu, and "Doctor Skuzzbucket" for Marik's father Hank. He is "your worst nightmare created in the flesh," and hates bad fan fiction where people "make him Yami Yugi's long-lost brother" and have no card games in it. Unlike Marik, Melvin does not have the special censor when Marik says the word "f***". When he says "f***", it gets censored the same way every other swear word gets censored.
In "Eternal Sunshine Of The Spotless Mai" when dueling Mai, he asserts that Mr. Tweetums was his best friend ever.
In "Requiem For A Nyeh", it is revealed that Melvin is actually working for 4Kids, as he is the single most evil entity on the show. This is ironic as Marik despises 4Kids. The most reasonable explanation as to why he sides with 4Kids may come from their shared hatred of Disney since live-action Disney films were a contributing factor to Marik's childhood abuse, resulting in Melvin's conception.
Melvin when trying to open the four digit code for a door tries to use the words "STAB", "KILL", "MUTILATE" and "PAIN" and remarks that they are the only words he knows.
In "Muerte Pinata", Melvin progressively gets angrier at the Pharaoh, finally culminating the first moment Melvin has genuinely snapped. Otherwise, he has shown a calm, if not manic behavior in the past, never getting angry to the point of a furious rant and instead offering more violence- i.e., when Joey told him to go "Hump a stump," and he delightedly chooses burning Joey alive as a way of killing him in place of asphyxiation. Also within the episode, Melvin displays cowardice as soon as the tables have turned when the Pharaoh summons Obelisk before he can recover from loosing Ra/Mega Ultra Chicken, quickly asking if they can "Play another game, like rock-paper-scissors". The Pharaoh chooses Rock, Melvin chooses "Umm", but Rock beats Umm and Marik regains control from Melvin. Melvin commands Marik to take the Pharaoh's power so they can rule the world together, but Marik refuses and questions how Melvin can rule over anything when he is "just an eyeball". Marik forfeits the match, leading to Melvin's demise.
Within the fanfiction LittleKuriboh has written, Melvin appears in Censored Town. Though he showed semblance of his typical personality, it is worth noting that Melvin within the fic is a lot more serious than usual; very akin to his canon counterpart. Though it is up for debate due to Censored Towns' ambiguous canon status, Melvin apparently often takes over Marik during the night, where he tries to kill Bakura in cold blood. Marik calls these 'Melvin Dreams', and they seem to aptly traumatize him. At the end of Chapter 5, he reveals he had taken over Marik and knocks Bakura out, leading to the 6th Chapter, where he threatens death and torture, commenting that his reasons for this were simply because it would hurt Marik. Due to the fact that he forces a kiss on Bakura within the fic, along with offhand comments in the series proper, such as in "Requiem For A Nyeh", ("I knew you always wanted me inside you, Bakura!") may imply Melvin has feelings for Bakura. This would make sense, considering Melvin is still a part of Marik's subconcious, and more outwardly honest about his emotions. Or, perhaps, he could be jealous.