Danny Phantom: The Ultimate Enemy is a video game for the Game Boy Advance console. It is based on the episode "The Ultimate Enemy" from the television series Danny Phantom and is the first video game for the series. Players play the role of Danny Phantom in his adventure to save Amity Park from a grim future where he fights himself.
The story begins ten years in the future in Amity Park. A rogue ghost tears down the city's powerful ghost shield with a mysterious power called Ghostly Wail. An adult Valerie appears to stop the ghost, and the ghost is revealed to be Dan Phantom: Danny Phantom's evil older-self. Somewhere in the Ghost Zone, two ghosts called the Observers have taken notice of the destruction of Amity Park. A ghost named Clockwork the Master of Time decides that he will make sure Danny never becomes evil.
In present-day Casper High, Danny is anxious about the upcoming Career Aptitude Test (C.A.T) that determines a person's future, since he has not had much time to study. Mr. Lancer announces if the person fail the test he or she will be doomed to a career at the Nasty Burger.
Danny returns home to FentonWorks where Jazz suggests Danny get to work studying. As the Fentons are working on a new ghost gadget "The Boo-oommerang" (a device that seeks out ghosts), a ghost suddenly appears behind Danny in the kitchen. The ghost reveals herself to be Box Lunch, the daughter of the Box Ghost and the Lunch Lady. Danny then transforms into Danny Phantom and defeats her - but damages the Nasty Burger in the process by causing the Nasty Sauce to explode. Danny finds a curious medallion Box Lunch left behind when she disappeared. Danny also accidentally phased through Mr. Lancer's briefcase where Lancer was keeping the C.A.T answer booklet. After finding the booklet stuck to his back, believing this is the answer to all of his studying problems.
Meanwhile, the Observers comment on this development revealing that they planted the test answers for Danny to find, hoping it will change him. The Observers are convinced Danny will still become evil because he made the wrong decision, but Clockwork insists otherwise.
Back in Danny's room, Tucker examines the medallion. Sam believes the medallion seems futuristic and then asks Danny what he plans to do with the test answers he found. Before Danny can debate about it, a ghost named SkulkTech 9.9 (the future Skulker and Technus combined) appears. After SkulkTech introduces himself, Tucker hacks into the ghost to intercept him. SkulkTech leads the battle back to the Nasty Burger and comments although "The Pummeler" does not work on Danny in the future, it will surely work in the present time. Danny is confused by this but he manage to defeat the ghost. Using SkulkTech's time medallion, Danny, Sam and Tucker arrive in Clockwork's lair where Clockwork reveals himself and battles Danny. Clockwork explains in the future, Danny has completely lost his humanity. The trio then conclude Danny's turning point was cheating on the C.A.T. Clockwork states he tried to change Danny's past, but since that did not work out, he will simply have to kill Danny. The trio then escape to the future.
They are surprised to see Amity Park in a state of ruin and then come across the future Valerie. Not realizing Danny is from the past, Valerie attacks him until Sam and Tucker stop her. Valerie is shocked seeing them and speaks that in the future they are both dead. The real Dan Phantom appears and Valerie tries to stop him but is defeated. Danny managed to save her and pass out. He urges Sam and Tucker to take off the time medallions and return to the present before Dan harms them. Danny is about to do the same until Dan fuses the time medallion inside Danny's body, trapping him in the future. Dan throws Danny into the Ghost Zone, then he travels to the past disguised as his 14-year-old self to ensure his past remain unchanged.
In the Ghost Zone, Danny encounters older-versions of Box Ghost, Ember, Johnny 13, and Kitty; including SkulkTech 9.9. When Danny thought he was finished he unleashes his Ghostly Wail and defeats them all at once. Then the Boo-oommerang hits his head with a note sent from Jazz ten years before; to inform him that Vlad Masters should have the solution to the situation. After finding Vlad's ghost portal, Danny meets an elder Vlad on the other side and Vlad explains what happened ten years ago and how Dan Phantom was created:
When Danny's friends and family (including Mr. Lancer) were killed in an explosion at the Nasty Burger by his alter ego because he was caught cheating on the C.A.T, he had to live with Vlad. Surprisingly, instead of trying to harm Danny he sympathized with his pain. After much mental suffering, he wanted the ghost half of him ripped out of his body. It was successfully done with the Ghost Gauntlets, but the ghost went berserk and ripped out Vlad's ghost half as well. Then the two merged into one evil ghost, that destroyed Vlad's manor and killing human Danny. Therefore, Dan Phantom was born.
Danny then asks for Vlad to use the Ghost Gauntlets to remove the time medallion from his body so he can return to his own time. In the present, despite Jazz's heroic actions, Dan lures Danny's family and friends at the Nasty Burger to repeat their tragic fate. Danny rushes to the Nasty Burger to have one final confrontation with his older self. He uses his Ghostly Wail, much to Dan's surprise, and traps Dan in the Fenton Thermos. Danny is about to go save his family when he is unable to transform into Danny Phantom due to exhaustion and couldn't save them in time. Fortunately, Clockwork appears and sets everything right again.
At school earlier today, Danny with newfound resolve, returns the C.A.T answer booklet to Mr. Lancer and he decides to allow Danny take the make-up exam the following week, preventing the tragic future. Jazz reveals her knowledge of Danny's ghost half, and is proud of her brother.
- Danny Phantom: The Ultimate Enemy video game
- DPOFPA Character Bios - Dark Danny