My son was sort of this way when we first got our Wi and he was that age too. Now he is almost 11 and although he will play and play and play if you let him- it is not the OBSESSION it seemed to be a couple of years ago.
Just stick to your guns with time limits and not allowing him to play everyday, etc. He will act all obsesso for a while and even complain about it and tell you how long his friends get to play, etc. but just be firm and don't change your rules.
Boys that age really like to draw cartoon characters- for some it is anime guys or superheroes, etc- for your son it is Mario! I wouldn't worry too much about that part of it. At least Mario is a fun and pretty harmless character.
As for other toys- not to be mean, but kick him outside! If my son has friends over and it is nice out, I do not hesitate to kick them outside with some lightsabers or a basketball or whatever! Video games are off limits at our house on warm sunny days. (of course this does not mean that my son didn't try to get over to his friend's house where he could play all day).
But seriously, just tell him 'Only bores are bored!' and give him 3 options for things he can go out and do or play. Either he picks one of those 3 things (and once he does and starts playing, he will have fun whether he thinks he will or not) OR he gets to help M. do chores. Pick something icky like cleaning the toilet bowl, and he will choose a board game or playing with toys or something VERY quickly!
Remember the M. phrase 'Video game time is a PRIVILEGE, not a right!!" I have said that so many times *I* was sick of hearing it, lol, but that attitude does seem to have worked.