- The aliens are here
They're out in force tonight
The aliens are here
We better keep out of their sight
The aliens are here...
Directed by Jim Stenstrum, Scooby-Doo and the Alien Invaders is the third direct-to-video installment for the Scooby-Doo franchise, produced by Warner Bros. Animation with a Hanna-Barbera Cartoons, Inc. copyright. Like the two films before it, Mook DLE did the animation.
The gang is driving through the Sonoran Desert when Shaggy sees a UFO, and in the ensuing chaos the Mystery Machine breaks down. After Scooby and Shaggy are chased into a nearby town by a pair of aliens, the gang is forced to take refuge overnight until the Mystery Machine can be repaired. In town, the gang finds a variety of colorful characters, some eccentric, some friendly, and some who may be something more. But it all comes back to the mystery revolving around the strange series of seemingly extraterrestrial threats plaguing the town - will the gang be able to uncover the mystery before they too end up as the aliens’ next victims?
Notable for being the last Scooby-Doo film to be animated with cels, as the next film and onward would be animated digitally.
- Accidental Kiss: When Shaggy and Crystal kiss at the end of his daydream, Shaggy ended up kissing Scooby in real time, and he isn't too comfortable with it.
- Anal Probing: It is very subtly implied by Lester that probing was what the aliens who captured him did to him before letting him go.
- Babies Ever After: In the last part of Shaggy's daydream, he and Crystal have a son who looks just like Shaggy, aptly named "Shaggy Junior". Scooby and Amber also have a litter of puppies that look like Scooby, with some of them having Amber's fur color.
- Born in the Wrong Century: Since the film takes place in the 2000s and Shaggy is the only one who still talks like it's the 70s, Alien Invaders makes it a plot point that he's into 70s lingo and the hippie style. This is why he falls for Crystal, a New-Age Retro Hippie disguise for an alien.
- Chekhov's Gun: Crystal's peace sign necklace; once she and Amber are in alien form, Shaggy spots this, allowing her to recognize it was indeed them.
- Comically Missing the Point: Lester insists he has pictures of the aliens and their ship, but they turn out to be paintings, not photographs as implied. He again passes this along to the feds when the captured scientists insist the aliens were for real. The gang laughs knowing the feds will not be impressed by what they see. The best part is the scientists think this will get them off the hook, unaware of what Lester actually meant.
- Cute Monster Girl: Crystal is still rather pretty in her true alien form.
- Darker and Edgier: Downplayed. The atmosphere is grimmer than usual Scooby-Doo fare with the threat of aliens lurking in the background, the mystery of what the government is up to, and the quiet town is a pretty bleak setting. However, see Lighter and Softer.
- Dark Is Not Evil: Crystal and Amber are quite intimidating in their true forms, but are still very kind.
- Did Not Get the Girl: Crystal and Amber are revealed to be aliens—they have to go back to their home planet at the end, and while they really like Shaggy and Scooby, they ultimately break it off, largely because they feel that a long-distance relationship wouldn't work.
- Disney Acid Sequence: "Groovy" is Shaggy and Scooby's idyllic, sweet as honey daydream about their love for Crystal and Amber, featuring them climbing mountains and borderline psychedelic imagery since both Shaggy and Crystal are hippie-age lovers.
- Embarrassing Hobby: Buck, a mechanic whom the gang consider a suspect, turns out to have been sneaking around to gather wildflowers. He didn't want anyone to know he collected pressed flowers because it didn't fit his tough-guy image.
- Exposed Extraterrestrials: When Crystal and Amber are revealed to be aliens, their true forms do not appear to have clothes.
- Evil Overlooker: On the official poster, an alien is overlooking Scooby as he is being abducted.
- Fooled by the Sound: At one point, Scooby and Shaggy discover a cave, and escape from some Military Police by having Scooby shake his tail while Shaggy hisses, creating the illusion of there being a rattlesnake.
- Aside from being just a tad out of touch with the times, it's obvious that none of Crystal's gear is of human origin, a clue early on that she and Amber are not of this world.
- After running off Shaggy, Crystal and the dogs, one of the M.P.'s growls "I wish we really could bust them." Providing a hint that they're not real M.P.'s
- Fourth-Date Marriage: Shaggy gets a song about his new fantasy of marrying Crystal, having children with her, and all that jazz within a few hours after meeting her.
- Greed: The primary motivation for the villains. Finding a mother lode of gold made them extremely greedy and they still kept their cushy jobs at the SALF station. In the climax they seize any opportunity to try to get even richer.
- Innocent Aliens: Crystal and Amber, despite looking intimidating in their true forms, are both of peaceful alien races.
- Interspecies Romance: Shaggy and Crystal along with Scooby and Amber because they're aliens, though they don’t realize it until after they’ve more or less professed their feelings for the girls.
- Laser-Guided Karma: Just as Scooby is about to wolf down a burger Lester knocked to the floor by accident, Shaggy downs it in one gulp. After years of stealing Shaggy's food, it's refreshing to see Shaggy beat him to the punch.
- Lighter and Softer: In comparison to the movie’s two predecessors. In spite of the grimmer atmosphere than usual for the franchise, it has the real aliens as the good guys and disguised humans as the bad guys.
- Manly Tears: Fred stars sobbing as Shaggy and Scooby say goodbye to Crystal and Amber.
- Mythology Gag:
- During Shaggy's song, and the subsequent daydream, there's a brief part that shows the rest of the gang in their original series outfits as they're all chasing a ghost in an old house. They even subtly throw in the original HB running and stopping sound effects from the 60s and 70s underneath the music. That's some attention to detail right there.
- During the song, Shaggy also mentions that he and Crystal would buy stuff from 1969, the year the original cartoon Scooby-Doo, Where Are You! originally premiered.
- New-Age Retro Hippie: Crystal the photographer is one. Or so it seems, until it's revealed that she's an Alien Among Us.
- O.O.C. Is Serious Business: After Shaggy and Scooby meet up with the others at the town's local diner, they're still so lovestruck after seeing Crystal and Amber that when Fred and the girls ask what they want to order, the Big Eaters claim they're not hungry and don't even order anything. Fred even grabs Shaggy's water bottle and sniffs it, apparently checking for booze.
- Real After All: Aliens are real, alright, but the ones we meet are the benevolent Crystal and Amber. Steve’s group posed as fake aliens.
- "Scooby-Doo" Hoax: Zig-zagged. The very human villains faked the main alien threat, while the actual aliens are disguised as humans.
- Star-Crossed Lovers: A non-lethal version. Shaggy and Crystal along with Scooby and Amber have to part ways at the end due to the girls being aliens from a distant planet.
- Suddenly Speaking: Crystal's dog Amber turns out to be able to speak shortly after the gang learn of the pair's true nature of being aliens.
- Talking Animal: Amber is revealed to be one at the end while in her dog form, much to the surprise of the gang. Fred comments on the irony, seeing how Scooby already fits the bill.
- Totally Radical: Crystal's even worse than Shaggy, seeming like she was plucked right out of the 1960s. Turns out her race discovered TV and radio transmissions from Earth in the 1960s and simply assumed that everyone still talked and dressed like that.
- Tsundere: Crystal's dog Amber was this to Scooby when Shaggy and Scooby met the girls, being aloof and dismissive toward him when he tries to show affection. She does eventually come to like him over time.
- Unmanly Secret: The gang is suspicious about the mechanic who's supposed to be fixing the Mystery Machine as he's extremely rude towards them and very secretive, and they find him alone out in the desert when he's supposed to be working on the van. He ends up being a Red Herring, but they're still curious as to what he was doing in the desert, so they decide to ask. Reluctantly, he reveals that he's been collecting and pressing wild desert flowers. He then explains he doesn't like to tell people about it because if they find out he has a soft side, they would walk all over him.
- Vile Villain, Saccharine Show: In spite of the Lighter and Softer tone, Steve, and to lesser extents the fake M.P.'s, Laura and arguably Max, have plenty of moments of sheer, Slasher Smile menace when they have the gang at their mercy and are trying to run down Crystal and Amber.
- Vitriolic Best Buds: Sergio the diner cook and Dottie the waitress throw a lot of insults at each other but seem to work well ok.
- Wham Shot: Crystal and Amber turning into blue-skinned aliens behind Shaggy and Scooby.
- Wrong Turn at Albuquerque: Shaggy makes a wrong turn onto government property courtesy of a sandstorm and then winds the gang up near Roswell after seeing a UFO.