Basic Trope: An extraterrestial invasion gets repelled relatively easily.
- Straight: Earth gets invaded by aliens from Pluto. Despite being at a severe disadvantage, humans manage to beat the invaders by blowing up their flagship, which somehow renders all alien forces inoperational.
- Exaggerated:
- Earth's atmosphere is toxic to Plutonians and they have no way of isolating themselves from it. Upon landing, they all die immediately.
- Plutonian ships cannot navigate in Earth's magnetic field. They all crash into each other before they even come close to the planet.
- Every alien species has a massive crippling weakness in their otherwise unstoppable war machines. Humanity's one advantage is that they have no disadvantages. Or more accurately, their crippling weakness is that they have no strengths either.
- Downplayed: Plutonian technology is quite vulnerable to electric shocks. Humans manage to exploit that weakness and eventually win, though not before losing millions of people in the war.
- Justified:
- The invading group of aliens was not an actual army, but a group of xenophobic zealots with no real combat experience. While they possess advanced technology, human leaders manage to outsmart them rather easily.
- Something about earth or humanity is an Outside-Context Problem to the Plutonians, leaving them with no defence against it, and no warning it was even an issue.
- Inverted: Humans decide to invade an alien planet, but forget to install proper air filters in their suits. All the invaders eventually die from alien diseases.
- Subverted: It turns out that the fleet humans destroyed was just meant to test Earth's defences and wasn't expected to achieve victory. When the main force arrives, it swiftly crushes all the resistance and conquers the planet.
- Double Subverted: ...but then humans form a resistance front and manage to completely wipe out the aliens by infecting their homeworld with flu.
- Parodied:
- Earth gets invaded by an easily-beatable alien fleet roughly once a week.
- The flagship is labeled with "To Save Earth, break glass."
- The Plutonian's weakness is massive and obvious to anyone with eyes-except to the Plutonians themselves, who stubbornly resist the efforts of other species to informs them of their Kryptonite Factor.
- The Plutonian ship gets stuck in fly paper, they're on the microscopic side of Little Green Men.
- Zig-Zagged: ???
- Averted: The Plutonians conquer Earth without much trouble.
- Enforced: The writers can't figure out a plausible way for humans to defeat the vastly superior alien army and they don't want to end the story with a Downer Ending. Thus, an easily-exploitable weakness is created.
- Lampshaded: "Well that wasn't very hard. You'd think an advanced civilization wouldn't have such stupid weaknesses."
- Invoked:
- The Plutonians' Mi-go masters engineer a weakness into them, to ensure they may destroy them instantly if they dare oppose their will. Unfortunately for the Plutonians, the humans are gifted knowledge of this weakness by a Mi-go who did it For the Evulz.
- The entire war is some sort of inscrutable alien test. By finding and exploiting the Plutionian's deliberately-placed weakness, humanity will pass.
- The Hero starts throwing random objects at the invaders in the hopes of finding a Kryptonite Factor.
- Exploited: The Plutonians leaders send troublesome generals to attack earth, in order to get them conveniently killed by those uppity bald apes and their mystery wonder-weapon.
- Defied: Nothing the humans attempt even slows the invaders, not even the weird stuff like cottage cheese or country music. The Plutonians have planned for every eventuality.
- Discussed: ???
- Conversed: "Anyone else frightened that humans have some sort of mystery weakness that no-one told us about? ...Anyone?"
- Deconstructed: It Only Works Once- and The Plutonians have more than one attack fleet. Earth is doomed, and it's inhabitants fleeting resistance is nothing more than a footnote in history.
- Reconstructed:
- While the Human-Plutonian war is far from over, the Plutonians have lost a major fleet to a battle they thought they'd win easily,and must spend some time recovering, both morally and physically. This gives time for the humans to recover, and reverse engineer more plutonian tech, giving them a fighting chance.
- The Plutonians discover that patching out their weakness isn't cost-effective enough to justify, and decide to cut their losses and invade elsewhere.
- Played for Laughs: The Weaksauce Weakness is utterly absurd: such as a brand of shampoo that melts Plutonian Power Armour into suds, leaving them metaphorically and literally exposed.
- Played for Drama:
- The Kryptonite Factor of the Plutonian invasion is Powered by a Forsaken Child- and the battered humans agonise over whether saving themselves is worth the price of a species-wide Moral Event Horizon.
- The impact of such an inexplicable defeat on the Plutonian psyche is explored in detail.
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