After some intense Googling, I found some really neat DIY Mario parties. I loved the decorations at this party at Zakka Life, and was inspired to make some of my own. They're made of posterboard and scrapbook paper. Easy, easy, even for a nondraw-er like me.
I also found a really neat pattern at Chica and Jo's to make Koopas and Goombas. (Lots of other cool Mario stuff there too. Check it out.)