Cadbury Creme Eggs have been a beloved Easter treat for years. Part of what has made them so special is their scarcity, being available for only a limited three-month timeframe leading up to Easter. But what if the delight and surprise of Creme Eggs could be transported into a completely different, but equally fun seasonal window – Halloween? It’s from this thought that the Screme Egg was conceived. As part of the product development, packaging was completely updated to fit the motif of the season with three iconic Halloween versions – vampire, mummy and zombie. Perhaps more important to diehard fans, the signature goo remained intact, albeit with a green tint.

Halloween is not a time of year that Cadbury has competed with any specialty product before. The time of year has no shortage of competition – with specially packaged versions of staple singles bars like “ScAero” and “Coffin Crisp” competing for share and display.

The overarching goal was to make a splash launching a new product that was somehow both new and familiar to people at the same time. The premise of a Goopocalypse allowed the brand to tell a larger narrative with the product at the forefront.

The good versus evil storyline isn’t just of-the-moment with the influx of everything zombie and vampire in pop culture, but also gave an opportunity to leverage the beloved and well-known character of the Creme Egg to launch their new Halloween counterparts.

First, Creme Eggs took to billboards, empty wall spaces and convenience stores around the country in the early fall. Just as humans would in a zombie apocalypse, each execution warned of the impending danger due to the outbreak of their monstrous cousins.

As time passed and Screme Egg numbers grew, escape became futile. The resulting battle between the two spilled out into streets, with the previous OOH pieces being overcome with mobs of Screme Eggs. The story unfolded on television and online in three episodic chapters. Appealing to the horror fan in all of us, the spots paid homage to famous frightful scenes from Return of the Living Dead, 28 Days Later, The Walking Dead, Resident Evil and even Thriller.

In the end, humans were encouraged to go to the Creme Egg Facebook page for ongoing Goo News reports, survival tips and sightings, all reported by the Creme Eggs themselves and written in their native tongue – Goo. Mirroring the real world infestation, this page was eventually overrun by Screme Eggs.

The campaign clearly resonated with consumers. Cadbury Screme Egg was the #1 category innovation in 2013 with $2.63 million in sales, growing the Halloween singles category by a whopping 154%. Not only did the 15-second episodic TV spots outperform Ipsos industry standards by 76% in terms of uniqueness, but the extended versions had over 200,000 combined views on YouTube. And in-store displays outperformed the industry average by 50%.

During the campaign period, the Facebook page grew over 600%. Engagement levels were even more impressive, with up to 24% of fans talking about the campaign. Some fans even became fluent in Goo, corresponding with the eggs in their very own language.

The Goopocalypse truly became a global epidemic, receiving love from all around the world on sites like Devour, Adweek and Fast Company. It even made waves in Japan with a full-page feature in prestigious design magazine, Brain.

Furthermore, the campaign was picked up by Cadbury U.K. and will be running in New Zealand this Halloween.