According to a widely cited 1999 study, medical error (the fancy term for "doctors and nurses f*****g up") kills as many as 98,000 people in the United States every year. A 2010 follow-up raised that figure to 180,000, and a 2013 one re-upped it to somewhere between 210,000 and 440,000, at which point they probably stopped doing follow-ups because it's too depressing. Since Mario is canonically a doctor (Dr. Mario, 1990, Gunpei Yokoi et al.), it's safe to assume that he has plenty of blood on his hands too.
This is aside from the blood on his feet, from all the Goombas he's trampled.
The World Health Organization says that medical errors "often involve drugs," so I've designed my Dr. Mario's Self-Medicating Journey level around the concept that Mario sneaks into a hospital and gets high as f**k on stolen medicinal mushrooms. The victim of Dr. Mario's medical malfeasance in this case is himself, since it's kinda difficult to jump over bottomless pits while tripping balls. (By the way, those of you who have Mario Maker can play this level yourselves with the code above. The rest of you will have to settle for GIFs.)
Each red X represents a place where a real player died, probably cursing
the state of modern medicine.