I remember this actually.
When I was 11, all of my friends (male that is) were obsessed with war. I suppose it has something to do with ignorance and the fact that they're getting close to the age where puberty kicks in and all of the hormones are just ready to be let loose. It isn't until the age of 14 or so that war simply dwindles to the occasional Call of Duty game here and there.
And leave it to Moppy to be a perfect example to my claim and use the two most horrible wars to say were his favorite. The civil war wasn't really that great, we had men killing brothers because they felt that they could own other men. And that was just the gist of it. WWII we had the genocides in Germany, the introduction of more powerful tanks explosives and weaponry, and not to mention we slaughtered thousands with the press of a button.
War is a cruel and horrible thing to enjoy. Grow up.
Also, Mario is the most child friendly character there is now a days. He does not need to be in a war. The most he needs to be doing is duking it out with his friends with a friendly no blood brawl.