The Lucky Helmet is a key plot element for the episode "The Helmet."
This helmet, made of scrap, has the appearance of a tin foil hat with tin foil wings and a rock attached to the center. It has the power to make whoever is using it very lucky, but if it is used too many times, it may drive its user madly dependent on the helmet, needing it for everything.
The lucky helmet plays a major role in its first and only appearance, "The Helmet." It was originally used by Gumball to perform party tricks. Eventually, he gets tired of it, lamenting about how succeeding at everything gets boring after a while. When Richard asks to borrow it to improve his chances of getting onto the game show Win or Don't Win, Gumball happily hands the helmet to him, and it demonstrates its power by immediately securing Richard a shot on the show. Nicole experiences its power as well, being notified by her employers that she is up for a promotion immediately after putting the hat on. An obsession with the helmet began manifesting within the married couple.
At school the next day, Gumball gets bombarded by a string of unfortunate occurrences. This, along with Darwin's side remarks of how he gave up such a useful trinket, leads Gumball to become obsessed with the helmet. Meanwhile, Richard tricks Nicole into letting him use the helmet, resulting in Richard winning a boat, and Nicole getting reprimanded by her bosses.
That night, Richard, Nicole, and Gumball savagely fight each other for possession of the helmet. Neither side is able to gain an advantage, and the fighting seemed like it would never end. Finally, Anais intervenes, using logic and reason to calm them down. It works - for Richard and Nicole, that is. They agreed that the helmet must be destroyed. Richard and Nicole restrain a hysteric Gumball, while Anais and Darwin head off to Mount Dump, to permanently dispose of the helmet.
At Mount Dump, Darwin is about to toss the helmet into the incinerator, but Gumball ambushes him and secures the helmet for himself. He places it atop his head and laughs as Darwin and Anais futilely attempt to knock the helmet off, being thwarted by Gumball's augmented luck. After a while, Gumball finally decides to retaliate. The helmet's power enables him to find both a tennis ball machine, a power supply for it, and a ton of ammo for it to rain down tennis balls on his opponents. He opens fire on his friends, and Darwin and Anais duck for cover. Then, in an act of heroism, Darwin charges through the barrage of tennis balls with a stale baguette, using it to deflect one of the tennis balls back at Gumball's head to knock the helmet off. He succeeds, and the helmet rolls into the incinerator. To Darwin and Anais's utter horror, Gumball jumps in after it. Fortunately, Gumball has not been incinerated - yet. Both he and the helmet were caught on a branch. Gumball struggles to reach for it, and with some difficulty, succeeds. Anais and Darwin attempt to pull him back up, but they need both of his hands to do this, and one hand was carrying the helmet. This meant that Gumball had to choose between the helmet, and falling into the fiery maws of the incinerator. With Anais's encouragement, he finally decides to let the helmet go. His second hand now free, Gumball reaches up to his friends' outstretched hands and gets pulled to safety.
It is not over yet, though - the helmet just barely misses the opening of the incinerator. The kids groan, then throw random objects at the helmet until it finally falls in and gets destroyed.