Have an awesome promo video and push face book. Every like you get will put that promo video on hundreds of ppl's news feeds.
Bobby Arel's "parade advertising" how much hype would you generate by walking two zombies around with chains through a mall? Or a local young bar scene?
The groupon would be awesome for new haunts, set on specific nights, early in the season. Think of the low ticket revenue as advertising costs. My mother told me about a haunt in the area she saw on groupon, so you never know who they will tell.
Target your marketing. If you're after kids and families, don't use bloody savage zombies for your parade, use a cute cuddly mascot creature, and hang out around the kiddie play area of the mall (just be sure somebody is with you so you don't end up looking like a perv lol)
People remember things they see in person, so make a huge impression and you'll be remembered.