So, a few years back, I found this dress at Goodwill:

It's '70s-retro and also Morticia Addams-slinky. Add a long black wig and a little Gomez arm candy and you're good to go. Bonus: The long sleeves and maxi length allow for layering underneath in case Halloween falls on a cold night.
Here's another take on the seasonal dress — Halloween/Day of the Dead without actually going all-out costumey:

This dress is a '70s/80s vintage pieces found on ebay. It doesn't have a label, but looks like a Gunne Sax gown from that era. It's almost a prairie dress, with it rows of tiny, emboridered, sorbet-colored flowers. But the dress itself, a sheer gauze layer over rustly taffeta, borrows enough Victorian elements (the high neckline, the gathered cuffs) that, in black, it's more Goth than Laura Ingalls. Pair it with high-button leather boots and an imposing hat and cut a spooky/intriguing figure at any party.