You wanna make a serious minded monster movie? Well, the result is going to be taken as symbolism, regardless of what you intended.
Here, then, are some of the standard Monsters from Our Monsters Are Different, with notable examples of said symbolism as interpreted.
Aliens (in general)
- Foreign people and other cultures.
- Sufficiently Advanced Aliens and other "Gods" - great power, interfering with humanity according to mysterious rules.
- Ambiguous Disorder or "oddness"
- Often sexually othered, allowing for such tropes as Discount Lesbians.
- Human imperialism and war.
- The original The War of the Worlds novel was largely meant as a critique of the British Empire and imperialism in general.
- Human reaction to disaster, similar to zombie films in that the people are more of a problem than the invaders. Also an element of all War of the Worlds adaptations.
Aliens or monsters who pretend to be human
- Conformity and infiltration are the watchwords here.
- Frequently associated with a Red Scare.
- They Live! uses it to represent Reagan-era consumerist capitalism.
- Some examples of this trope will draw comparisons to anti-Semitic conspiracy theories, as that particular strain of racist gibberish follows similar tropes as these stories. (John Carpenter's They Live! is occasionally interpreted this way by neo-Nazis. Carpenter has colourful words for the Misaimed Fandom.)
- Human interaction with nature and Romanticism Versus Enlightenment— cryptids are usually described as living in areas of untouched wilderness and hunted by humans with fancy technological gizmos. Heroes often have to help them escape and be left alone in the wild, without human interference.
- Tintin in Tibet ends with the hero saying he hopes humans never catch the Yeti, because they'd only put it in a zoo.
- The Unicorn has an very similar status even though it doesn't have exactly the same history or reputation as the modern cryptids. Unicorns may be mysterious even in settings where other fantasy creatures are an ordinary fact of life.
- If bought from an exotic country to the modern world (as in King Kong), it can be anti-colonialism on top of environmentalist.
- Destructive Greed — Western dragons hoard treasure and are usually portrayed negatively.
- While largely a Forgotten Trope in the secular world, older Western stories, particularly Medieval ones, tended to use them as a metaphor for Satan or paganism (or Mohammed or Islam, which tended to be lumped together by storytellers of the time). See the story of Saint George and the Dragon.
- Disasters. Either man made (Hedorah, giant robots, mutants) or natural (Rodan), a sort of divine retribution tied to shinto beliefs can also be read into it (Mothra).
- Godzilla has basically been all of the above at some point. He started out as a metaphor for the devastation of the atomic bombs dropped on Hiroshima and Nagasaki. Godzilla, Mothra, King Ghidorah: Giant Monsters All-Out Attack! has him being the collective manifestation of the souls of those who lost their lives during Japan's Pacific campaign in World War II. Godzilla (2014) gives him a Gaia's Vengeance characterization on top of being a radioactive mutation.
- Abuse of military power. Almost always military might will fail miserably and just waste everyone's time, and often it's the fault of the military that the Kaiju are there in the first place.
- The threat of Nuclear Weapons and other weapons of mass destruction. Nuclear Fallout.
Former humans in general (that keep their intelligence/personality)
- The Five Stages of Grief. See Stages of Monster Grief and Tragic Monster for more.
- Loss of identity and place in society
Former humans in general (that lose their intelligence/personality)
- The inner dark side of mankind
- A descent into madness or obsession
- Being unable to "move on" from some wrong—usually consumed by anger or sadness
- A ghost may be so fixated on this wrong that they forget everything else about themselves—hence, the dangers of dwelling too much on something in the past
- Being so attached to the physical world that they've ruined their own spiritual health
- The way that the injustices of history influence the present. These events can range from the scale of horrific colonial crimes and entire socioeconomic systems (such as in the Indian Burial Ground trope) all the way down to interpersonal family conflicts that haunt the minds of their descendants (such as the ghost in Hamlet).
- Anything to do with parasitism or disease, including:
- Who Wants to Live Forever?
- Too many Vampire Detective Series to mention
- Vampires Are Sex Gods—don't judge by appearances, because the people who seem the slickest, the wealthiest, the coolest are in fact the most heartless
- Bloodthirst as a metaphor for drug addiction
- The need to kill to survive
- Strangers who seem scary at first but are actually harmless, in the case of the Friendly Neighborhood Vampire who needs protecting from Van Helsing Hate Crimes. This tends to show up in more light-hearted works, naturally
- The Beast Within
- Metaphor for STDs
- Metaphor for menstruation
- Metaphor for addiction, since the classic werewolf loses control during transformation
Zombies (apocalypse / plague type)
- Post-apocalyptic works in general are about how humans react to the fall of civilisation, so over the course of the story the focus may move from the ravages of the zombies to how the survivors are harming each other.
- Mindless, ravenous consumption
- Survival of the Fittest
- Faceless conformity and loss of identity
- Epidemics, especially when zombieism is The Virus.
- Metaphor for mindless consumerism.
Zombies (necromancy / voodoo type)
- Again, faceless conformity and loss of identity
- Fear of being Buried Alive
Artificially intelligent machines and robots (in general)
- Slavery - the word 'robot' is derived from the Czech word for 'slave' - or workers in general, which also makes them useful for talking about Communism. 'Robot revolution' stories - whether the story was on the revolution's side or not - were especially common in the early half of the 20th century, but fell out of fashion once revolutions stopped seeming likely and the Cold War began. Red Scare stories featuring robots in this era will often suggest they are disguised perfectly as humans, hiding amongst humans and spreading evil robot ideas. Even fairly apolitical robot stories tend to depict them as 'lowly' characters compared to the humans due to their life of drudgery, which sometimes allows them to be Servile Snarkers or even so beneath notice as to be able to commit murder...
- Dependence on technology and possessions - the idea that a possession, in some way, owns its owner. Or, less frighteningly, the idea that a possession might have a 'soul'.
- The meaning of human consciousness, humanity or the soul. In stories like this, robots are often depicted as being essentially 'human' and with consciousness but condemned to be treated as a 'thing' due to their artificial minds. They may be fighting to gain the rights of being recognised as human, which can be read as a metaphor for civil rights movements. Alternatively, the robots and artificial intelligences might have Blue-and-Orange Morality, demonstrating that a being doesn't have to be human to be intelligent.
- Romanticism Versus Enlightenment, when a highly intelligent but emotionless robot is pitted against less intelligent but loving human beings.
- The failings of rules and law compared to intuitive thinking - in stories like this, robots will be incapable of disobeying seemingly harmless rules, resulting in awful consequences in messy real world situations.
- Destiny - a robot is usually made for a specific purpose, with abilities to allow it to do its job, and often with the inability to choose not to fulfil that purpose.
- Anxiety about death - robots can't be killed due to not really being alive and tend to invoke the Uncanny Valley (the lowest point on which is an animated corpse). See the skeleton imagery in The Terminator, or how this is spelled out as a reason for instinctual human hatred of robots in Doctor Who's "The Robots of Death".
- Much like with the kaiju above, giant robot imagery is often connected with nuclear weapons, being obscenely powerful weapons that should never be used. Far and away more common in Real Robot works and more horror-inflected fantasy fare, though optimistic Super Robot works are certainly not unknown to touch on this (i.e. The Iron Giant). In some stories, the robots may literally be armed with nukes, as in Metal Gear.
- Teamwork, unity and The Power of Friendship, if the robot requires multiple pilots that work together, or a synchronisation with the spirit of the machine. In more consciously political works, this can be turned to more down-to-earth feelings of community spirit or civic responsibility (as in Patlabor, which is mostly focused on the robot pilots getting stuck in traffic jams or complaining about paperwork).
- In more fantastical robot stories, a kind of mind-body-spirit relationship - the robot is the body, the pilot is the mind, and the more fantastical elements of the robot (e.g. becoming strengthened by force of will or emotion) represent spirit.
- Works influenced by Neon Genesis Evangelion (of which there are many) will often incorporate Freudian concepts into the robots. In Evangelion itself, the focus is on motherhood (and the pain of an extended childhood), with the bodies of the robots keeping their pilots safely in biomechanical, fluid-filled womb-like cockpits; other works may interrogate other pieces of Freudian imagery such as phallic cockpits or weaponry.
Grey Goo and nanomachines
- The potential for new technology to make people obsolete
- Green Aesops about the impact of industry on the environment
- Unforeseen Consequences of Human Industry/Technology
- The dangers of being blinded to risk by the potential benefits of a new technology