Rodney can invent different devices by collecting a certain amount of blueprints scattered throughout the environment. In the beginning of the game, he repairs his Wonderbot, his personal companion. He also obtains the Scrap Launcher from Herb Copperbottom, a weapon which uses Scrap as ammo which is found in the worlds of the game, and a wrench which is used as a melee weapon. More weapons are acquired throughout the course of the game. Scrap is also used to purchase items at vendors, including the Maxi-Scrap 500 and Maxi-Scrap 1000 which upgrades his Scrap capacity from 200 to 500 and 1000 respectively, the Refine-O-Max which doubles the value of Scrap, and four mutually exclusive upgrades to his Scrap Launcher which can be replaced at any time. Later while in Robot City he obtains the Magnabeam from Jack Hammer, which uses energy which must be refilled by going on recharge circles, and can also be used as a weapon.
The GBA game functions as more of a Metroidvania-style game, where Rodney has to platform and fight enemies across a sizable world map, collecting upgrades by beating bosses and finding parts scattered across the city for different robots also scattered across the city. The weapons you gain open new areas of the map.
There are a handful of small minigames as well, from a game where you toss oil cans at customers to surviving a torrent of dominos. The fast travel system, taken from the film's transit system, also has a small mini-game where you can collect extra ammunition for weapons.
The scrap launcher remains from the console ports, though you obtain it through delivering an item in the first area rather than getting it from one of the movie characters. The Magnet Bomb attracts enemies closer to it and hits certain switches, and an Electric weapon that does the most damage and hits certain switches. Upgrades can be found for each that allow them to do more damage and have a longer range.