Just pick-up the exclusive 5-pack from Target ‘The Avengers Age of Ultron’ to get the Ultron exclusive. The set is $17.99 for the 5 cars which is slightly higher then the individual packaged cars. The good thing is all 5 cars are different than the single pack release. Mostly just the wheels are changed but other subtler differences can be found. Check out the Marvel character cars to see side by side comparisons.
