In Fat Princess, the player joins one of two opposing groups consisting of up to 16 characters each, with the goal of rescuing their team's princess from the other team's castle. To make their opponents' task more difficult, players can feed the captive princess cake slices. With each slice, she becomes heavier and harder to carry back to her respective castle. Over time, the effect of the cake wears off.
Players can change their character classes and abilities by picking up hats that are generated at their team's castle. Hats can also be found on the warzone where enemies have fallen. The game's six classes are the villager, priest, mage, warrior, ranger, and worker with three additional classes (pirate, ninja and giant) unlocked from DLC. Each class has its own unique set of abilities and skills. Classes can be upgraded by having a worker collect resources from the map and then upgrading the hat-producing machines. Upgrades provide alternative weapons or attacks to each class.
On each map there are several trees and ore nodes that worker classes can use to obtain resources.
Other interactive objects are bombs, potions that turn players into chickens when thrown, and torches that most classes can use to ignite their weapons to do additional damage.
Source: Wikipedia, "Fat Princess", available under the CC-BY-SA License.