Plankton has a robot-carolers army coming towards the Krusty Krab in the winter. Help SpongeBob protect the Krusty Krab. The gameplay is an overview perspective of SpongeBob standing at the top roof of the Krusty Krab while robot carolers are coming to the building in all directions. The player uses their mouse to control SpongeBob's aim and clicks to throw snowballs. Throwing snowballs at robot carolers will knock them out into the snow ground. Try to prevent any robot carolers from getting inside of the Krusty Krab building. At first, it only takes one snowball to knock out each individual robot. But when the game progressively becomes harder and different types of robots appear, it takes more than one snowball to knock them out. There are power-ups in the game to help the player. When a power-up picture appears, throw a snowball at it to use the power-up. The Electromagnetic Pulse power-up is a jellyfish that will eliminate caroling robots on 1 side of the screen. The Gary Time power-up will slow down the robots for 20 seconds, making it easier to knock them out one by one. The Super Snowball Thrower power-up is a Reef Blower that can throw faster and more rapid snowballs. However, the Super Snowball Thrower power-up only lasts temporarily. The player must tap their spacebar to initiate a snow blizzard to clear the screen of caroling robots. At the start of the game the player is given only 3 snow blizzards to use, but they can get more by touching the Snow Blast power-up. Plankton is shown with a remote controlling the robot carolers through a magnifying glass in the left bottom of the screen. When robot carolers get inside the Krusty Krab, a noise meter on the right bottom of the screen starts filling up. The Krusty Krab gets louder as more caroling robots go inside the building. The Noise Reducer power-up will reduce the number of noise in the Krusty Krab. If the noise meter becomes full, it's game over. The player can also quit the game by going to the menu and pressing the quit button.
Some versions of the game include an advertisement for Jingle Brawl being released on December 26, 2009. This is due to Merry Mayhem! and Jingle Brawl both being released on Nickelodeon website in December 2009.
When the noise meter fills up, the game audio becomes louder.
Approximately, it takes 9 caroling robots getting in the Krusty Krab to completely fill up the noise meter.
Sometimes when the player eliminates the robot carolers, Plankton in a magnifying glass can be seen raging.
When caroling robots are getting inside the Krusty Krab, Plankton in a magnifying glass can be seen laughing.
In the gameplay, Plankton's robot carolers are heard singing a "Merry Christmas" song.
Depending on what level in the game the player quits, one of two different game over screens are shown.