9. Kitty Pryde
Being one of the youngest ever members of the X-Men after joining at the age of 13 - Kitty Pryde definitely wasn't one of the team's heavy hitters. After all, there are only so many walls a girl can walk through.
But fans always knew Kitty was capable of much more. An adult Kitty was able to project her conscious back through time into her younger self during the Days of Future Past arc. This was the first time she demonstrated having other abilities and provided a glimpse at what her full potential might be.
Kitty has gone on to become one of the most relatable X-Men characters in the current run, blossoming into a confident, mature, and extremely capable hero. Kitty even ended up joining the Guardians of the Galaxy and adventuring off-world for a time. But she eventually returned home and became the newest leader of the X-Men, eventually becoming the new Red Queen as the leader of the Marauders.
Although Kitty was able to phase an entire planet after using The Black Vortex in her adventures with the Guardians - her core strengths remain the same. Her humanity and compassion - coupled with her incredible intelligence - are the chief factors that make her the total badass she is today.
Being able to speak the dialects of both the Shi'ar and Skrulls is pretty impressive for an earth-born human after all.