I think the witch robes are pretty.

Concerning the horror aspects, I think SE is largely worried about their under age audience. Kids these days know what alcohol is, etc, and most of the swearing is said in round about ways that many kids simply won't understand. Things like realistic gore, scary stories, jump scares and other things commonly associated with Halloween might be too scary though. Heck, even a lot of adults really have issues with those sorts of things.

My favourite FFXIV Halloween event has to be one from a couple of years ago that had imps asking lore based riddles with multiple choice answers. It was fun figuring out the answers, and if you couldn't figure them out yourself you often learnt a little of the lore you didn't know about before as you looked them up or eliminated options. I did that for ages and they had a lot of riddles so it was always interesting ^_^