Had a strict no killing rule, broke it by killing the Marauder questioning all his beliefs.
Destroyed a perfectly farm good tractor saving his sister in Giant Sized X-Men #1, I mean, his father must have really loved that tractor.
Illyana loses her soul, gets manhandled by a demon at the age of 8 (correct me if I'm wrong).
She loses control of Limbo for like the millionth time.
She gets reverted to a child, and killed, then reborn, and then I'm not sure what happened from there but now she's a demon child again.
Mikhail Rasputin turns out to be alive and a leader of a remote land,
Commits suicide 15 issues after they found him alive.