Time stop. One way i can see it not being an instant death for the one who presses the watch is if time isn't technically stopped but you are instead moving on a different plane of reality. But that wouldn't really be time stopping i feel.
I feel like flight is the one that everyone wishes for, but would be most likely to kill/harm you.
What if you pass out at a certain height? Get severe anxious or can't breathe at a certain altitude? What if you get something stuck in your eye and can't see where you're going? What if your shirt flies over your face and you can't fly and fix at the same time? I don't think it would necessarily be an instant-death thing, but I see the potential in getting killed before you can practice your powers enough that you'd have plenty of experience dealing with this stuff.
I suppose you could wear pilot glasses :-D I agree with you though. Imagine flying into a little bird at 200 mph. It would be like a bullet of feathers.
Yeah, flying into a little bird at 200 mph got me thinking about the ability to move at super speed like Quicksilver or The Flash. What if he run into a fly or a mosquito at seemingly 9,000,000 mph (as seen in the X-Men movie)?
Even an accidental stumble like The Flash did in Justice League movie at that speed would probably broke, or worse, decapitate his leg completely. It would also catapulted the rocks into everybody in vicinity.
I saw a number of fictional powers that could do that. On the show "Heroes," two of the deadliest powers were causing people to die all around you when you got scared, or creating miniature black holes that could suck you in. Another I saw on that show was the ability to freeze anything you touched, and what if you froze yourself and someone smashed you?
The deadliest fictional powers are usually the ones that tax the user. It's disturbing when you see the person suffering nosebleeds, brain damage, part of their life-force is used up (causing them to age prematurely), metabolism might go up and cause them to lose too much weight, or there's internal bleeding due to the stress of their powers. Or worse, they become psychotic from using their abilities too much, forget who they are permanently, and become so dangerous their friends are forced to kill them out of mercy as well as saving the world, despite the cost of losing someone they care about.
The scariest scenario is when a magic-user is forced to allow a demon or evil spirit possess them so they can unlock their most powerful abilities; but it's a terrible setup, because they have no guarantee that demon will give them back their free will after the possession occurs. Or worse, the demon will turn the mage's body into a monstrous instrument of destruction and wreak havoc that was never part of the plan. I have never enjoyed watching Faustian bargains like that. It never ends well, even for those with the best of intentions.
The one thing that has stuck with me from Heroes is the girl who had rapid healing and did all sorts of nasty things like sticking her hand into a grinder and such. It would be one of the best powers to have though if you could stand the pain.