It is a strategic puzzle game, with a boy protagonist Niko, who is joined by friendly monsters in his quest against the evil boogens. Niko is initially alone, but is soon joined by monsters, each of which has a unique ability such as burrowing in dirt areas, charging down brittle obstacles, freezing water so rivers can be crossed, or shattering crystal with piercing shrieks. Control can be switched between Niko and monsters. Niko can buy different outfits, some of which have special powers. He can also collect coins to buy items or fetch treasure to return to grateful villagers or monsters. There are four regions to explore outside of Niko's village.
Source: Wikipedia, "[en.wikipedia.org/wiki/Monsters_Ate_My_Birthday_Cake Monsters Ate My Birthday Cake]", available under the CC-BY-SA License.