Menma looks virtually identical to Naruto, though his blond hair has become black as a result of merging with Tobi, and he wears it in a longer and more shaggy-looking style, similar to his father's. He also lacks the Eight Trigrams Seal and has darker, more feral-looking whisker marks, and dark circles under his eyes.
When initially appearing as the mysterious "Masked Man," he wore a white kitsune mask, a dark blue-gray robe with gray lining and a fur collar, and a tattered gray-blue cape emblazoned with his personal emblem: nine reddish-brown circles of varying sizes arranged in a cross pattern, atop a larger green-grey circle. After revealing his identity he discarded the robe and mask, beneath which he wore no shirt, fingerless opera-length black gloves wrapped in studded red-brown leather straps, baggy black pants, and red-brown sandals.
Abilities
Menma's abilities are essentially the same as Naruto's, to the point of creating a darker version of the Rasenshuriken. He also seems to have better control over Kurama, as he was able to create living beings composed of its chakra. After merging with Tobi, he gets a Sharingan in his right eye, allowing him to predict all his opponents movements and copy any techniques.
Trivia
"Menma" is the name of a Japanese condiment which is also found in ramen. This is a parallel to where Naruto's name originates.
Menma's personality can be compared to that of Dark Naruto.
Menma's ability to control multiple entity's composed at once is very similar to those of Pain and Kakuzu.
Menma is the only character whose name is different from his Dimensional Counter-part.