I have knowledge of two mechanic-specific injuries that were told to me second hand by other mechanics who witnessed them happen.
1) Getting popped in the face by a shock absorber. This injury could kill a man instantly. When you put a car up onto the lift, and yank the tire off, and expose the brakes and the shock absorber, things can happen. Depending on what's broken or loose, and depending on what's stuck solid and in need of your rubber mallet, and depending on how careles you are when you start unscrewing things and/or malleting things, the shock absorber could discharge right at you, shooting its inner rod straight at any part of your body like a small javelin.
2) Pulling an arc out of a live car battery. This can also kill a man instantly. While a faithful husband will wear his wedding ring day and night, a smart mechanic always takes off his ring and his wrist watch and his St. Christopher's medal and any other metal jewelry before he goes within 12 inches of a car battery. The third worst thing that can happen with car batteries is a mechanic might be trying to loosen the hex bolts that hold down the negative and positive cables. And he will of course try to do this with a crescent wrench --which is a wrench made entirely of metal and which will span your entire hand, and which will make firm contact with all four fingers and your thumb IF you are holding it correctly. And if he allows the metal wrench to make contact with any other piece of metal on the car (such as the frame) he might pull and arc out of the battery, passing the electrical charge through the crescent wrench, across all four fingers. And IF he's wearing is wedding band, he could very well lose that ring finger by literally frying the finger clear off. The second worst thing he can do is he can just plain electrocute himself, and so he might wind up just plain dead. But the absolute worst thing that can happen is the battery will explode, not only sending hot molten shards of plastic battery shell into his face, but also sending a huge spray of battery acid into his face.
I know you said you aren't looking for fatal injuries. But you might want to consider a toned-down, "whew that was close!" version of either of these two accidents.