Hank McCoy is the Beast. Probably the most prominent character from the books to appear in the film – after Prof X and Magneto) and present in X-Men: Last Stand (played by Kelsey Grammar (Frasier) and introduced as an old friend of Professor X). He presents difficulties in that his CGI / Make up is intensive stuff but is a welcome addition to what is a unnecesarily attractive cast for mutated misfits. However will always be the most difficult character of the X-Men to bring fully to life on the big screen. This trailer suggests that Matthew Vaughn might’ve puled it off but without a full reveal who can say.
Emma Frost is / was one of the most challenging characters in the X-Men canon (unprecedented student death toll under her tutelage, unofficial psychic sex therapist to the team, former enemy and the only girl who could take Scott Summers way from Jean Grey – before she died – again) but looks like she’s been reduced to that of a bit player in this trailer. Emma Frost is in alliance with Shinobi Shaw as White Queen to his Black King of the Hellfire Club in the books. Simplified here, Frost looks like she’s a minion. Though to waste a character like Frost seems unlikely – particularly given her introduction in Origins: Wolverine.