Followers of the Facebook role-playing game can pick up free Santa hats from the in-game store, as well as limited edition candy canes and reindeer horns.
Developed by Bossa Studios, the Facebook video game adaptation of the BBC television series entered open beta in October, amassing more than 250,000 users since release.
The role-playing social game involves players travelling across Camelot, fighting monsters and levelling up. It features real-time co-operative play, allowing players to explore quests with six other friends.
Since its launch, the development team has added in-game chat, character animations, the ability to view friends' profiles and additional weapons and equipment statistics for items.
The team has also introduced the brand new 'March of the Dead' mission and added the spoon as a usable weapon after it appeared in the recent series.
Bossa Studios' creator-in-chief Imre Jele had previously told Digital Spy that Merlin: The Game will also be accessible to those unfamiliar with the show.
"Not everyone knows the TV show," he said. "So we've designed it in a way that if you know the show, you're going to find a lot of little things that are relevant for the game."
Merlin: The Game can be accessed on the title's official website.
Watch a trailer for Merlin: The Game below: