2. Kitty Pryde
Not technically from Singer's time, but let's allow it anyway. Like Wolverine, Shadowcat plays an instrumental role in the "Days of Future Past" comics the movie gets its title from. You can bank on there being major deviations between the source material and the final film, but it's hard to imagine this iconic story without this iconic character at its heart. Arguments have been made for Jennifer Lawrence's Mystique taking over the Kitty Pryde role, and it's not the worst idea in the world — but when an actress with Ellen Page's pedigree is an option, why not bring her back into the fold and move closer towards the original material? Win-win for everybody!