Rayman: Hoodlums' Revenge is a game that was released exclusively for the Game Boy Advance in early 2005. It takes place shortly after the events of Rayman 3: Hoodlum Havoc and, like its predecessor, pokes fun at the platformer video game genre. It and Rayman Raving Rabbids for the Nintendo DS are the only 2.5D platformers in the Rayman series.
This game is the first Rayman game to use an isometric (2.5D) view. Most of the levels put the player in control of Rayman, while other levels put the player in control of his partner, Globox. In certain levels, the player is able to control both of them in the same level by pressing the Select button to switch the characters. The goal of each level is to get to the end and gain the maximum amount of points possible. To do this, the player has to collect gems and lums that are scattered throughout the levels. Also, freeing Teensies and defeating enemies gives the player points. At the end of the level, the player earns Murfy stamps, based on their score. Murfy stamps are not important to the completion of the game, but after getting a certain number of them, extra levels are unlocked. There is a total of five levels that can be unlocked with the acquiring of Murfy stamps.
Source: Wikipedia, "Rayman: Hoodlums' Revenge", available under the CC-BY-SA License.