WARNING: This article contains spoilers for Extermination #2 by Ed Brisson, Pepe Larraz, Marte Gracia and VC's Joe Sabino, on sale now.
When Hank McCoy plucked the Original Five X-Men (Cyclops, Jean Grey, Iceman, Angel and Beast) from the past and brought them to the present-day, he couldn't have foreseen the teens sticking around as long as they have. Also, he more than likely didn't anticipate the physical and mental changes they'd undergo while fighting alongside their grown-up counterparts.
Just a few examples of how the young X-Men have changed since leaving the past are Jean's power levels evolving, her taking the role of leader on the team, Iceman coming out as gay, Beast's interest in magic over science, and Angel's wings evolving thanks to the power of the Black Vortex. Of course, this also doesn't take into account the things the X-Men have learned about their grown-up selves, with adult Cyclops becoming mutant public enemy number one with the humans, and Jean discovering she's died a time or two.
However, the one X-Man who is still alive and may have undergone the most drastic changes is Warren Worthington III. Angel had his wings brutalized decades ago during the "Mutant Massacre" crossover in Uncanny X-Men #210-213, resulting in Warren needing to have his wings amputated. Suffering from depression at the loss of his mutant gift, Angel lets the X-Men villain Apocalypse prey on his weakness by offering to give him his wings again with one caveat -- Angel has to become one of Apocalypse's Horsemen of the Apocalypse. From that moment on, Angel was gone and the Archangel was born, complete with blue skin and lethal metal wings.
After becoming a pawn of Apocalypse, Warren would eventually be successful at purging the evil influence from his body, but the Archangel would always rear its ugly head time and time again. In Uncanny X-Men #338, Warren's body changed yet again when his metal wings mysteriously shattered to reveal his natural, feathery wings underneath.
A very important part of Archangel's saga occurred during Rick Remender's run of Uncanny X-Men, when Apocalypse's influence took control of Warren yet again, leading him to attempt to become the second coming of En Sabah Nur. Psylocke, Warren's former girlfriend and lover, was able to help him through this tough patch, but Warren would lose part of his memory in the process, with a more pacifist personality being born.
Again, all of these transformations happened to the adult Angel, with his younger counterpart only gaining cosmic wings. However, a traumatic act committed upon young Angel in Extermination #2 mirrors one of our examples above.