"The Ultimate Enemy" is a special episode numbered as twenty eight and twenty nine as well as the second TV movie of Danny Phantom. Danny gets caught up in a time traveling adventure. There, he discovers a future where his family and friends have been killed and he has become the most powerful and evil ghost in the world.
Ten years in the future, Amity Park is a bustling future metropolis protected by a large ghost shield, operated and run by Damon Gray while his 24-year-old daughter, Valerie Gray serves as the city's sole protector from ghosts, particularly one who uses his newest power, the Ghostly Wail, to easily break the ghost shield and conquer the world. Valerie flies away on her hoverboard, only to be further ambushed by the Fright Knight who's now in servitude to the ghost that broke the shield. She heads to safety in the Fenton house, now occupied by her and her father. Unfortunately, the powerful ghost gets through from below and blows up the entire house. All this is being watched by Clockwork, ghost master of time as the mysterious Observants explain to him that the powerful ghost is Danny Phantom ten years into the future. Clockwork's job is to destroy the current Danny Phantom to ensure he never grows up to be the world's most evil ghost.
Back in present time, Lancer makes a public announcement to everyone in school about the CAT which will help determine their future, one test Danny takes seriously. Jazz already passed with flying colors while another classmate named Irving failed, later defending his job in the Nasty Burger, saying that if the boiler is messed with in the wrong way, the entire place would blow, something none of the students care about. Lancer then locks the test answers in his briefcase, going as far as handcuffing himself to it. Clockwork watches all this from his headquarters while the two Observants push him to destroy Danny (since they only observe and never act). Clockwork obliges.
Back home, Jazz tries hard to help Danny succeed, but this makes him even more frustrated about the fact that she's smarter than he ever will be and how little success he feels he will gain. He is then hit by the Booo-merang, a Fenton boomerang device designed to home into a ghost's unique ectosignature, something which it keeps doing with Danny. His parents grow confused on why it keeps targeting Danny, then take off with it.
Clockwork comes and freezes time, then sends Box Lunch (daughter of the Box Ghost and the Lunch Lady Ghost) after giving her a time medallion to ensure her stay in another time period from the future to destroy Danny. Jazz quickly leaves upon seeing the ghost to let Danny handle the situation and the two fight, eventually flying all the way to the Nasty Burger where his friends and Mr. Lancer are. Battling inside, remembering Irving's words, Danny throws a condiment sachet towards Box Lunch and heats it with his Ghost Ray, causing the Nasty Burger to blow up halfway (and the boiler room inside to slowly rise in heat), sending Danny back to where the masses have gathered, where he goes straight through Lancer's briefcase upon turning intangible for safety. Once everyone runs away in panic, Danny finds the time medallion Box Lunch had been wearing before being sent to her own time period upon losing it, as well as the answers to the CAT test. As a result, with the Observants pushing him, Clockwork sends another ghost to fight, even though he claims that the future is sealed.
The next day in school, Tucker and Sam berate Danny for his possible plans to cheat on the CAT, something Lancer overhears. Opening his suitcase to find his test answers gone, he calls for Jazz to talk with him after school where he reveals to her that Danny must have stolen the answers. Jazz tries to defend him, stating he has no proof, so Lancer gives Danny time until the day of the test to return it.
Back in the Fenton household, Tucker tries to figure out the time medallion's functions, but gets no results. Danny then gets ready to look at the answers to the test (much to his friend's dismay) until he meets another ghost from the future: the combined forces of Skulker and Technus, into Skulktech 9.9. A long battle between them ends when Danny's powers are shorted out by Skulktech and then gets captured by one of the hunter's mechanical claws. Tucker hacks a way into their system, causing them to fall onto a lamp post, their time medallion slipping off as well, sending Skulktech as well as Danny, Sam, and Tucker - who tried to pry the claw off of their friend - to Clockwork's lair.
Inside, the trio finds the only portal to the future, witnessing the destruction Danny's future self is causing over there. Tucker then finds a few time medallions and puts one on in a failed attempt to go back to the present. Clockwork then appears seemingly wanting to kill Danny to prevent his dark future. Danny tries fighting Clockwork, but with the advantage of controlling time on his side, it's a one-sided battle the ghost nearly wins. Stopping all time, he lunges out to slay the time-frozen Danny with his scythe. Unaffected by the time-out, Tucker figures out that the time medallion protects the wearer from all sorts of time-based altercation. After he gives one to each Sam and Danny and frees them from their freeze, Clockwork decides that they have seen too much and summons other iterations of himself to prevent them from altering the timeline. With nowhere else to go, the trio escapes through the portal to the future to get away from Clockwork.The future already proves grim for the three and even more so when future Valerie catches young Danny, ready to exterminate him. Sam and Tucker step in to stop her, only for her to be shocked at the prospect that they are alive. Dark Danny then appears and sends Valerie away, rescued only by Danny, and then passes out. In the meantime, Sam and Tucker run away, only for Dark Danny to drop the rubble of the Fenton house on them with his Ghostly Wail. Before they are hit, Sam takes off their time medallions, safely returning them to their own time period.
Sam and Tucker end up in an alley near the Nasty Burger where Jazz confronts them, having discovered Danny indeed had the test answers. She warns them, saying that she'll talk to Mr. Lancer if Danny doesn't confess. Afterwards, Sam theorizes that Danny cheating is what will lead him to become evil. Back in the future, Danny finds out his family, friends, and Mr. Lancer were all killed when the boiler exploded with them inside. Dark Danny afterwards comes to him, telling his past self that he plans to ensure his future still exists. To bind young Danny to this time, he places his past self's time medallion inside of him, unreachable by either ghosts or humans, and throws him into the Ghost Zone to keep him from causing any further distraction. Then, disguised as the 14-year-old Danny, he uses one of the time medallions to travel back into the past.In the present time period, the disguised Dark Danny reunites with his former friends, telling them both he has beaten his evil self and that the Nasty Burger boiler is also taken care of (when in reality, it's still ready to blow). Back in the future Ghost Zone, Danny meets up with all the ghosts he has defeated previously, all the worse after having encountered Dark Danny (Johnny 13 is in a wheelchair and pushed around by his shadow, Ember McLain is overweight and has severely damaged vocal chords, etc.). As an act of revenge, they gang up on him.
Back in the present, Dark Danny returns to his room and meets Jazz who confronts him on his cheating, later confessing she knows he is half-ghost, and proud of what he does, until now. A bit surprised that she knew, Dark Danny turns into his normal form, prompting Jazz to finally figure out he isn't Danny, seeing as how even the Booo-merang wouldn't home in on his ecto-signature. Dark Danny confirms that he is her brother and that his past self is floating in the Ghost Zone in the future. Jazz defiantly claims that her brother will beat him, Dark Danny claims that he highly doubts it. He tells that he destroyed the Fenton portal in the future and has yet to find the one belonging to his "cheese head of an arch-enemy" (which Jazz guesses to be Vlad Masters) and stuns her unconscious.Jazz wakes up the next day to find Dark Danny has already left to take the test. Quickly, Jazz takes the Booo-merang and ties on a note she hastily wrote with her headband, sending it to the Ghost Zone in hope it'll reach Danny in 10 years. Back in the future, Danny is helpless against the ghosts attacking him. In his frustration, he suddenly gains the ability to use the Ghostly Wail, knocking them all unconscious. Afterwards, the Booo-merang finds him. Danny reads the note, realizes that Vlad is involved and goes to track him down. Meanwhile, Dark Danny starts to cheat on the test, something his friends still are livid over. Jazz watches from afar, ready to destroy him with the Fenton Ghost Peeler, only for Dark Danny to notice, sending an invisible duplicate of himself to knock her unconscious and drag her away.
Danny manages to find the portal to Vlad's manor, but upon entering, he notices that the manor is long gone and the once proud billionaire is now a depressed old hermit. Seeing Danny and guessing that he's from the past, he tells the story of how Dark Danny came to be: After the death of his loved ones, Danny moved in with Vlad, as he was the only one who could possibly understand his pain. Wanting to make the hurt go away, he requested Vlad to remove his ghost half, something Vlad honored, pulling it out with the Ghost Gauntlets. However, once Danny's ghost half was removed, it went berserk, took the gloves and ripped Vlad's ghost half out of him. Danny's ghost half then attempted to overshadow Vlad's ghost half, only for the two ghosts to mix and Vlad's evil half overwhelming Danny's good half becoming the evil incarnation it is now with Danny and Vlad watching in horror. Blowing up Vlad's manor, and supposedly killing Danny, Dark Danny left to begin his ten year rampage of world destruction. With the story over, Vlad laments that he spent the ten long years stuck in regret and guilt for all the damage he had caused. Danny, in a rare moment, forgives him, then asks for his help to take out the medallion inside of him using the Ghost Gauntlets. Readying his gadgets, Vlad remarks that perhaps he could eliminate Danny before he becomes evil instead and strikes.
Dark Danny has finished his test and walks off, prompting Lancer to call his parents and arrange a meeting at the Nasty Burger, together with their son. There he reveals his suspicions that Danny cheated, shocking his parents badly. Sam and Tucker then come over to warn them that the boiler is about to explode while Jazz, completely in Fenton Ghost Peeler gear, reveals Dark Danny's true form to the others. Alarmed, his parents are on the offensive, demanding to know where their son is, only for Dark Danny to reveal himself as their child. He smugly taunts the fact that his parents, the world's two leading ghost experts, couldn't figure out that their own son is half-ghost (Jack tells Maddy that "for the record, he blames her").
Dark Danny points out that there even was a rhyme between Fenton and Phantom and that Jazz was the only one to figure it out, much to Tucker and Sam's surprise. He then ties up his family, friends, and Mr. Lancer to the boiler where the explosion would kill them. Danny then comes from the future with a bunch of Fenton gadgets, ready to duke it out with his darker future self.
A battle rages and Dark Danny ensures the battle drags out long enough for Danny's friends and family to die in the explosion, believing that the fact he still exists is proof that he shall be Danny's future. However, he grossly underestimates his past self, as proved when Danny suddenly uses the Ghostly Wail on him. Shocked that he already gained a power he should not get for another ten years, Dark Danny is struck by another Ghostly Wail, causing him to crash into a building. Danny then sucks him up with the Fenton Thermos. Unfortunately, with the last wail taking a lot of his energy, Danny cannot transform back into his ghost half, making it too late for him to stop the explosion.
Time freezes however, and Danny finds himself next to Clockwork who has saved his loved ones, now knowing that the time master knew everything that was to happen. He explains to Danny that the Observants view time as a parade, watching each event happening in sequence, whereas he sees the parade from above, where all the twists and turns might or might not happen. Giving him a second chance, Clockwork sends Danny back into the past before the start of the test where he returns the test answer booklet and then confesses he was going to cheat, much to the relief of his friends and sister. Given another chance to take the test, he goes out to the front of the school where he gets Jazz to confess that she knows his secret. With that said, the two embrace, Jazz now part of Danny's team. He then goes off to fight off a giant ghost nearby. As they do battle, Jazz is splatted with ectoplasm, and comments that "this is going to get some getting use to".
Back in Clockwork's home, the Observants cry out to Clockwork, stating he cheated to influence Danny's choice. Clockwork answers that true, he cheated, but stating Danny made up his mind on his own despite his little cheat. The Observants then claim that he is to be the sole guardian of Dark Danny now that he exists outside of time. Clockwork merely agrees, saying that he knows everything that has happened and will happen, then he places the thermos away, where Dark Danny struggles in vain to escape...
- Allusions: See List of allusions
- Goofs: See List of goofs
- Many fans consider The Ultimate Enemy to be the darkest episode in the entire series.
- Introduced Ghost Powers: Ghostly Wail
- This is the third time in the series where Danny's ghostly and human halves are separated. The first two are in "What You Want" (which was purely accidental) and "Identity Crisis" (where Danny did the separation himself).
- This also marks the second time Danny turns to the dark side (the first time being "Control Freaks").
- This episode is tied with "Maternal Instinct" as Butch Hartman's favorite Danny Phantom episode.
- This is the second Butch Hartman TV movie in which the protagonist meets his older self from an alternate future. The first was "Channel Chasers," a Fairly OddParents 90-minute-long TV movie. Timmy's older self was masked for most of his screentime, and his constant pursuit of his younger self led young Timmy to believe the figure was a villain. The respective older selves also time-travel in the respective episodes.
- There is a major time travel logic flaw. Danny turning evil is dependent on him cheating on the C.A.T and his friends and family being killed in the explosion, yet he (his future self) causes them to be killed. It would be illogical for someone's evil form to cause the event that caused them to turn evil in the first place, although this could be seen as an example of predestination paradox. Further, because Danny had discovered the full story of Dark Danny's origins from talking to Vlad in the future, it is likely he would know not to go to Wisconsin and undergo the procedure of having his ghost half removed. However, since the Observants have asked Clockwork to prevent this future, it's possible that the original explosion was caused by a different event, thus Dark Danny was trying to undo Clockwork's attempts to prevent it.
- The future Vlad never explained how the Nasty Burger exploded, but it's shown that Clockwork sending Box Lunch then SkulkTech 9.9 to fight Danny are what causes it in the episode. The explosion from the fight with Box Lunch puts the heat lamp close enough to warm up the vat of Nasty Sauce, then the battle with Skulltech pushes it even closer, speeding up the process.
- It is revealed that the phone number of the Fenton Works is 555-1221.
- Dark Danny is Danny's unlockable costume in "Nicktoons: Attack Of The Toyboys" but the costume being named "Evil Danny."
- This is the first and last time Jack calls Danny "Dan" (while he's studying for the CATs).
- This episode reveals that ghosts age and can have children (Box Lunch).
- This episode was ranked #10 in the 100 Greatest Nicktoon Episodes countdown, and was the highest-ranked Danny Phantom episode in the countdown.
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