3. Detroit Steel
Detroit Steel, which first appeared quite recently in 2010 in Iron Man (vol. 5) #25, is not actually a character, it's simply an armour. Marketed by Stark Industries' rivals Hammer Industries, the armour is available for hire to the highest bidder, meaning that anyone who can afford it can wear it - which makes it pretty meaningless as far as a villainous identity goes. It can be spray-painted to suit the wearer's preference and has been painted in a Japanese flag design, while it has also been said that it could have the McDonald's logo on it if the price was right. In addition to the identity problem that would come with using Detroit Steel in a movie, it would also inevitably receive criticism for resembling a Transformer (much like Avengers received criticism for the giant Chitauri space whales resembling some of the crafts from Transformers: Dark of the Moon, which preceded the Avengers movie by a year). And, again, if Marvel must use an armoured villain again, at least make it further removed from previous efforts than this one, which offers nothing new.