At one time, Spider-Man tried to cure himself of his spider-powers with a homemade cure. It failed, and gave him four extra arms, which I think is pretty impressive. Sure, his formula doesn't cure spider-powers, but it does grow extra arms - there's got to be a market for a drug like that.
The RecipeSpider-Man is made from a Spider-Man Minimate, four extra Minimate arms and four shoulder pegs. The arms were painted flesh-colored, then snapped onto the extra shoulder pegs that were glued onto Spider-Man's torso.
Special thanks to all the customizers who did this first, like drgnrbrn316, TBT, and any others I've forgotten.