I have never been in Dublin on Halloween but I can confirm that Halloween up in Derry, Northern Ireland is off-the-chains amazing! Lots going on in the city, from family-friendly day/evening events to more partying. I'd recommend doing a simple YouTube search for Derry Halloween to see the Halloween parade. Plus I realized when I was there that so many of these traditions originated on the Emerald Isle, so cool.
I went for the first time in 2019 and planned to return the following year but of course could not (thanks, COVID), so I'm going again this year!
I'm guessing Dublin won't be lacking on Halloween stuff either, though. Honestly, I can't imagine not having a good time in Dublin on any day of the year. Have a great time, wherever you are on October 31st. :)