Now, I don't know much about marketing, but I came up with this concept for an ad image to accompany an opening day campaign in the tradition of "Mortal Monday." Not to toot my own horn, but I do believe it's quite the slam dunk.
Alternatively, I considered the following, but I decided that it was a little too obvious and cute, which was not really what I was going for:
Alas, it's probably a bit late for Marvel to arrange this for the movie release. But I would even propose that Marvel should retire the "Avengers Assemble!" battle cry in the comics, instead replacing it with "Avenge somebody." Here are some mockups I put together as examples to show how well this could work: