Going back to the elections earlier this year, it's worth mentioning Katie Wilson's defeat of Bruce Harrell in the Seattle mayoral election.
While Seattle isn't nearly the size of NYC, her election surprised me much more than Mamdani's. Harrell is a moderate Democrat. The two biggest things I disagreed with him on was that he was more aggressive on clearing homeless camps and that he refused to put in traffic calming measures (speed bumps, cross walks) on a road near my house that is popular with pedestrians and bikers. Wilson, is okay with being called a Democratic Socialist, had pushed for a payroll tax, had previously pushed for defunding the police, and is big into mass transit. I don't think she's ever held public office. I'm not sure if this Facebook post will show, but she had previously been struggling with daycare expenses. She may be the most surprising mayor of a major city that I can think of. Of the People, by the People, for the People.
Facebook post picture below.
"After much deliberation and a grueling interview process, I’m pleased to announce that I’ve accepted a new job and will not need any financial support from my parents to cover the high costs of childcare going forward. #AmericanDream #thisisyourcity"