Alex Kidd in Miracle World is a classic action-adventure game that follows the story of Alex Kidd, a young boy who lives on the planet Aries. Seven years ago, he studied Shellcore, an ancient art that allows him to break rocks into pieces, and now he's leaving Mt. Eternal to travel to his spiritual homeland when he learns that the peaceful city of Radactian is in danger. The city is threatened by Janken, the Emperor of Janbarik, who has sent his henchmen to prepare for a game against Alex. If Alex loses, he will be turned to stone and vanished forever. To save Radactian, Alex must first defeat Janken by winning three games at the game of Janken.
The gameplay involves exploring eleven locations, each with its own unique dangers. Alex can collect coins, which can be used to buy items such as a motorcycle or power bracelet, helping him get through each location. He must also avoid traps like ghosts and collect the Telepathy Ball to read people's minds.
As Alex progresses, he learns that Janken's behavior changes after winning the game against his henchmen. If Alex wins, they decide to play dirty. To overcome this challenge, Alex uses his fists to fight off some of Janken's enemies or performs the "Shocking Waves of Destruction" with the power bracelet.
Before facing Janken, Alex must rescue his brother Egle from imprisonment and obtain a letter and two medallions. With these challenges ahead, Alex's quest to save Radactian becomes even more difficult.