X-Men: Dark Phoenix - 8 Mistakes It Must Avoid
2. Bringing Back Emma Frost
The Hellfire Club, introduced to the X-Men movie universe in First Class, plays a major role in the Saga as the Earth-based catalyst for Jean Grey's transformation.
Emma Frost, in particular, has a hand in breaking Jean's mind, but bringing back January Jones's scantily-clad version of the mutant would be a huge misstep.
Although she was killed off screen during the events of Days of Future Past, the soft reboot this film ushered in means Simon Kinberg could recall her if he chooses.
Except he should avoid doing that because Jones was horrible for the part, looking dead-eyed and disinterested throughout First Class' duration.
This is where the director will have to get creative with the characters he does have at his disposal. Case in point, Psylocke is blessed with similar powers and could deputise for Frost if the Hell Fire Club is deemed essential to the adaptation.