Sandman (also known by his civilian name as Flint Marco) is a super villain/anti-hero in the Marvel comics universe mostly seen fighting Spider-Man.
He was a common thug who, after robbing a bank, ended up hiding in a bomb testing site. He ended up being caught in the blast of an experimental bomb, but it did not kill him; it instead made his body into sand. Using this power to his advantage, Flint then proceeded with his crimes, until he was stopped by Spider-Man. Sandman is a lot different from the average goon. While he does partake in villainous activities, he cares for his mother and robs only because he needs to. Sandman has been a member of the Sinister Six in the past, and has even joined heroic organizations, like the Avengers and the Wild Pack.
One of Spidey's incredibly gritty rivals has made it to M.U.G.E.N with gameplay influenced by the Marvel vs. Capcom series. Sandman's A.I and gameplay is very deadly and top-notch, especially in the hands of experienced players.