The popular free-to-play online card game "Hearthstone" will get a new expansion pack on Dec. 7. The brand new expansion pack is titled "Kobolds and Catacombs." It is reported that 135 new cards will be added along with other features such as spellstones and some unidentified items.

According to a former report from Game Spot, the expansion comes with an added single-player content that includes 48 new encounters, legendary weapons, and card packs.

The "Kobolds and Catacombs" trailer was uploaded to "Hearthstone's" YouTube channel on Nov. 3. The official description reads: "Legends tell of a vast underground world and the countless treasures that lie in store for worthy adventurers! Gather your party to explore Kobolds & Catacombs..."

The trailer itself begins with narration. "Legends tell of a vast underground world and the countless treasures that lie in store for worthy adventures. You've signed up the best, you're on a great quest to find the mighty mother lode. There is treasure galore, but perils in store and construction that is not up to code."

After the initial introduction, the trailer continues on providing a glimpse of the underground catacombs. It also promises loot and rewards galore for those who are brave enough to venture inside and overcome the perils. While the rewards are great and plentiful, so are the threats that players will encounter in the forthcoming pack.

Aside from being filled with prizes and the treasure, the trailer revealed that the Catacombs would be filled with different enemies too. The enemies inside ranged from giant rats to fire-breathing dragons. An assortment of various monsters who are just waiting for unprepared adventurers to fall into their claws are added as well.

"Kobolds and Catacombs" is "Hearthstone's" fifth expansion pack. "Hearthstone" is free and playable on PC, Android devices, Apple phones, and tablets. It was initially released in March of 2014 and has gained popularity ever since.