10. Darwin - X-Men: First Class
There's no denying that the immediately evolving mutant from Matthew Vaughn's wonderfully revisionist franchise "rebirth" was a particularly arresting moment - and a nice confirmation of Sebastian Shaw's capacity for malevolence - but it was actually more problematic than it was entertaining, and it robbed the franchise of one of the better, more useful mutants.
Darwin was a bad-ass, though under-used and played rather oddly as a semi-comical figure, and though it allowed for some impressive CGI gymnastics, the dead-meat tag should have gone to someone else. Like Banshee. The problems with the decision to kill Darwin are two-fold: firstly, and probably most frustratingly, it inevitably attracted accusations of tokenism and of conformity to the rather distasteful cliche: the Minority Dies First trope.
Though he was a smartly conceived character, his death retrospectively made him no more than a red shirt, and for a film that purported to be so invested in socio-political undertones, that is a little difficult to take. Secondly, in purely narrative terms, Darwin's death didn't really make sense.
He becomes the only character to effectively have his primary mutation limited, despite being introduced as being able to evolve to cope with "anything". Given that power, he should have been one of the most powerful mutants in existence, and his self-preservation instinct should have meant killing him was basically impossible.
Consider the World War Hulk comic: when confronted with the revelation that he can't absorb Hulk's radiation, Darwin's self-preservation mechanism told him the best thing to do was run away - so why the hell did the film version of the same character swallow? He could have very easily evolved the ability to close his throat, or to spit, since EVERY HUMAN CAN ALREADY DO THAT.