One of the most memorable characters in the original trilogy was Mystique, the blue-skinned shapeshifter played by Rebecca Romijn. Of course, a cameo by Romijn in "Days of Future Past" is far from out of the question: not only did she make a blink-and-you'll miss it cameo in "X-Men: First Class" (Jennifer Lawrence's Raven briefly morphed into her in the "bed scene"), Romijn could also use the work, frankly. It would also be interesting to see Romijn's more hardened future version of the character come face-to-face with Lawrence's naive budding supervillain.

- Chris Eggertsen