Bill de Blasio is up for re-election this year.
AMNewYork has a listing of currently declared candidates. de Blasio will almost certainly be in a Democrat primary against multiple opponents. I expect there will be a GOP primary as well.
The only candidate right now that I find interesting is Republican businessman Paul Massey. I don’t know what his position on 2A is and, from a purely practical standpoint, it doesn’t matter. With a huge Democrat enrollment advantage any Republican running would need access to an equally huge source of money. Massey does seem to be making some inroads in that area. See, “Better call Paul: Massey adding muscle to mayoral campaign” and “Massey Beats Out Mayor With $1.6M in Campaign Funds Raised in 6 Months, Spends Even Bigger.“