6. Vision
In the comic books, Vision is a creation of Ultron, making his emergence very easy to include. He is made for use against Ultron's own creator, Dr. Hank Pym - though that would obviously have to be changed (perhaps to Tony Stark, if he is the reason Ultron exists in the Marvel Cinematic Universe, or the Avengers in general) in the movie. Vision is a very powerful being, possessing complete density control of his own body, ranging from invulnerability to complete intangibility. He can also control his mass, ranging from extraordinarily heavy to complete weightlessness - he utilises this ability for phasing into beings and objects and then solidifying as a means of molecular disruption, causing pain, damage or death and destruction. He can also fly and possesses the ability to project solar energy (via his eyes or a solar jewel on forehead). He can interface with computer networks and possesses superhuman strength, intelligence, reflexes and senses. As an artificial being, he is also capable of self repair and regeneration. He could initially serve as a troublesome foe for the Avengers before they persuade him to join their ranks in future movies (as has been rumoured for so long - in fact it was previously rumoured that Agent Phil Coulson IS Vision).