I love to make costumes for all 6 of my kids, my 4 year old loves a pillow & bag I made for him out of a Mario print, and playing Mario games. I try to make them with things I have on hand or can acquire - cost of new materials for this Homemade Little Mario Costume - FREE!
I was most concerned about the hat, but I found this wonderful pattern on the internet that made that easy. I dug through my fleece fabric, and had just enough red and white fleece to make the hat. The 'M' I took from the Nintendo website from a photo, then transferred it to my PC and blew it up real big, and printed it and used it as a pattern to cut it out. The red circle was the leftover center. Glued it on with white glue. Super easy, and fast.
Overalls were next. I picked some bright blue water proof fabric from my stash. Tough to sew with but perfect for a cold Halloween night to stay warm and dry. I used my old stand by patterns from Kwik Sew - the sewing for Toddlers book. There was a perfect overall pattern that needed no design adjustments, except to use snaps that pound on in seconds instead of buttons, which also lets him fasten it. Then I cut some bright yellow felt in a large circle and sewed it over the snaps to look like Mario buttons.
I couldn't find knit gloves in white for a kid, so I traced his hand, made the fingers fatter and 3 attempts later had gloves that he could get on made of white ribbing knit.
Off to his drawer to find a red shirt. Because of the cold, we ended up putting a sweatshirt and red windbreaker over the top which gave him a nice puffy look, a little more Mario like than the skinny guy he is.
We drew on the mustache with black dry-erase marker, which washed off easy. He looked great running around house to house. It seemed he ate a golden mushroom!