Iron Man Mech (above) is an official LEGO Marvel Superheroes set.
After I gotten hold of this set and built it, I noticed the legs were kinda short, so I decided to lengthen it by one (and finally two) stud high. (below).
After some more tinkering, I managed to create an alternate vehicle mode for it. No additional parts are required for this mod.
The Vehicle Mode
Follow the steps inside the video I prepared below. Have fun!