"Destiny"'s upcoming Halloween event, Festival of the Lost, has not been announced in any recent update patch notes. That doesn't mean that it isn't coming, however; it just looks like an announcement hasn't been made yet, but there are already some items made for the event.
GameSpot has the lowdown on the Festival of the Lost gear, thanks to the hacking and data mining efforts of Ishtar Collective, a "Destiny" fansite. Among the Halloween things they were able to find in the game were a new sparrow, shaders, consumables, masks, and emotes, although there is no in-game photos or concept art yet; just thumbnails and names to go on.
The new sparrow is a green one, while the new emotes are the appropriately Halloween-themed Howl and Terrify and the new sparrow is a bright green color. Meanwhile, "Destiny" patch 2.4.1 released this week did enable the ability to get back masks you've previously gotten before into your inventory. New masks in this year's event include those of SIVA, Ghost, Aksis, and Lost Prince. Some items from the previous years of Festival of the Lost, including masks and consumables, have also been updated, but it's not sure yet as to what kind of cosmetic changes they received.
So what is known about this year's Festival of the Lost? For one thing, most "Destiny" players have been theorizing that Festival of the Lost will be the same event it was last year. It's mostly going to be doing quests while wearing a Festival mask.
Since "Destiny" developer Bungie wanted to focus more on the update to the increased Light cap after releasing a Heroic mode for Wrath of the Machine, Festival of the Lost hasn't been announced yet. But as the Halloween is a little under two weeks from now, expect it to be announced sooner or later as they don't have that much time left.