10. Kraven The Hunter
On first glance, Kraven the Hunter isn't anything too special when it comes to the "power" department because... well, he doesn't have any superpowers to speak of. When you get right down to it, he's just a man who shouldn't pose any significant threat to a superpowered hero like Spider-Man.
Anyone who thinks that upon meeting the man would be about as wrong as possible because Kraven is anything but powerless. While it's true that he doesn't have superpowers per-say, he does possess a special elixir given to him by the Voodoo priestess, Calypso, which enhances his senses, slows his aging, and improves his strength.
It's a sort of cheat, to be sure, but it enables the already gifted hunter to take on the world's most dangerous game: Spider-Man. In his hunt for our Friendly Neighborhood Spider-Man, Kraven has done some rather horrible things, which elevate him from a powerless human to ruthless villain rather easily.
In an early story, Kraven shot Spider-Man and buried him in a grave where he remained for two weeks. During that time, Kraven took over his role and did some nasty things. When it was over, Spider-Man rose from the grave and found that Kraven committed suicide — his task complete, but he wouldn't remain dead for long...