Cady is the 16 years-old daughter of two zoologists stationed in Africa. Her mother receives an invitation from Northwestern University, and the whole family goes back to North America. Home-schooled since her childhood, Cady is the new girl at her high school, where she must learn how to survive on that aggressive social environment.
Mean Girls: High School Showdown is a basic RPG with tile-matching battles, similar to Puzzle Quest. At the beginning, the player has to choose an avatar from a selection of four teenage girl stereotypes, and then distribute 15 points between five attributes: charisma, intelligence, endurance, luck and strength.
After picking one of the available skills, special abilities that can be used during play, the game starts with the first tutorial battle. The combat occurs on a separate screen, showing at each side two columns containing portraits of the fighters' avatars and a list of the acquired skills, with a grid filled with assorted tiles occupying most of the screen at the center. Two meters frame each portrait, one for loyalty and the other for stamina. The objective is to either fill the enemy loyalty gauge, or empty the stamina one.
Each combatant takes turns swapping adjacent tiles, trying to make matches of three or more of the same type. The tiles have specific uses. The whip takes away some of the enemy's stamina. The heart fills a portion of the loyalty meter. The other tiles fill four buttons at the top of the skill list. Each skill requires a number of points from one of these buttons. Special tiles, like the wild card that matches any sequence of tiles, or the chameleon that duplicates adjacent tiles, appear randomly on the board. A new skill is available after every four levels.
After the battle, the game shows a map of the high school with the avatar figure superimposed walking over it. Two icons at the bottom, a ? and a !, give access to lists of pending quests and sub-quests, respectively. Clicking on the list entries makes the avatar move towards the quest location. At the top right, a portrait shows how the character is developing. Depending on how each battle is won, the character can lean towards good or evil, affecting the game's ending.