We've done a useless character with Leena Toros, how about a pointless character.

Matt is Mello's friend, he likes computer games, is quite lazy and is the 3rd most intelligent out of Wammy's orphanage behind Mello and Near.
He begins by failing to keep track of Misa Amane, Mogi and Aizawa, then in a final scene he's shot dead during the kidnapping of Takada.
His entire manga presence is 12 panels while his anime screentime is 69 seconds, barely over a minute long.
His popularity in the fandom is odd, I suppose he's a good character to work off for a prequel but even then, his impact on the story is so low that you wouldn't miss him if he were cut, especially when you consider Mello is the type of character who wouldn't have friends with his horrific inferiority complex.
It's even suggested by the author that Matt was created just to give Mello a friend.
So that's Matt. Side characters in OVAs have more impact than he does.