Dogs can be attacked in Dandori battles. However, if they run out of health, they simply go inactive for a few seconds before reappearing at your base.
As always, friendly plant-creatures Pikmin will be hunted down and eaten by predators on-screen if the player does not collect them before nightfall. Oatchi the dog is never left behind in gameplay or cutscenes. Moss, a dog native to the planet, is unable to leave with the cast but finds a new purpose. A third dog has a tattered collar, though it's unknown what happened to its original owner.
Medication is administered to astronauts suffering from a strange disease. It's done entirely offscreen, with the only visual cue being a small pill icon counting the number of doses collected.
You will be leaving a lot of dead enemy bodies on the ground if you don't want your Pikmin to take them back to the onion to spawn more Pikmin (which is most of the time, so expect to walk past plenty of dead bugs).
Several major and minor enemies are modeled after spiders; though most of them are rather abstract, there's a species of enemies called "Dweevils" whose appearances are close enough to real spiders to potentially be a problem.
There is an enemy species called a "burrowing snagret" that is part serpent. It has the head of a bird and and pops out of the ground, wack-a-mole style.
It doesn't move like a snake, and it's body isn't particularly long, but it does have a scaley body.
Leaflings are PNF-404 visitors who have been sent into a special onion and turned into leafy monsters. Olimar has fallen victim to this off-screen, and he in his new Leafling form subjects another visitor to this.
If a pikmin that isn't blue goes into the water (ice and winged pikmin can float above it but not go in) they can drown, which is a form of asphyxiation. You have a chance to save them by whistling though.
If a Pikmin is electrocuted, it will spasm on the ground for a few seconds and potentially die. Both the player and their dog can be stunned or knocked unconscious the same way.
Several enemies have eye-stalks that can be targeted by Pikmin. Depending on the enemy, this can cause the eye to grow redder over time, and eventually shrivel up. No blood or gore.
There are a lot of bulborbs/bulbears surrounded by younger bulborbs (though many of these aren’t actually related to the larger, as dwarf red and orange (and possibly other) bulborbs are just mimics), which you can kill. The Empress Bulblax is explicitly a parent, and she is actively birthing bulborb larvae (you read that right) during her second fight.
You can see ghosts arise (and quickly vanish) after pikmin and enemy deaths, but it’s unclear if this actually happens in universe (as it could just be for making it clear the creature is dead). Some enemies are ghostlike, and ghosts are mentioned in some post-day text. Glow Pikmin, while ghostlike, are explicitly stated not to be ghosts, instead being made of light.
No screamers, especially loud noises, or images flashing across the screen. Some bosses and enemies hide underground, in the ceiling, or conceal themselves in normally 'safe' items until the player is within striking distance. This tends to scatter your Pikmin and/or make them shriek in panic and may be upsetting for younger players.
One/a couple of the caves has a bathroom tile aesthetic similar to the "shower room" from pikmin 2, but no actual showering takes place. There are also sprinkler hazards which rain water down on an area.
Of a sort. Leaflings are stranded astronauts infected with a strange disease. While not strictly possession, it compels them to kidnap others, convert them, and obsess over a certain minigame. It also causes memory loss after the fact, so the distinction may be thin for some.
Enemies that are actively hurting Pikmin have louder sound effects to cue the player in. It varies from enemy to enemy, but you can usually expect a loud crunch, a swallowing sound effect, and the Pikmin shrieking and wailing.
Treasures you collect may seem to be destroyed in the process of harvesting Sparklium, but you can see the treasurer holding onto them, so it's more likely that the objects simply have their Sparklium extracted and then kept safe after.
No hospital scene, though much of the game revolves around finding and curing astronauts suffering a strange illness. Cures are administered off-screen and are accompanied by a bottle-opening sound effect.
Several characters are from Koppai, a planet where the residents are over-eaters incapable of realizing when they are full. The planet is stated to be on the verge of famine, but unlike Pikmin 3, this isn't the focus of the story.
The player and blue or glow pikmin can go underwater, and are often required to in order to retrieve treasures, enter caves, etc. The player’s dog will eventually learn how to swim on top of water, but cannot at the start of the game. Pikmin other than blue pikmin or glow pikmin will drown in water, but can be whistled back to be saved.
While not particularly loud, several bosses and enemies conceal themselves or hide inside treasure until the player gets within striking range. Usually accompanied by a monster roar and the Pikmin shrieking and may be upsetting to younger players.
When throwing Purple Pikmin, or when a particularly heavy enemy stomps on the ground, the camera shakes. I believe this can be turned off in the settings, however.
Nothing too heavy, though Olimar does question whether he's the one controlling the Pikmin, or if the Pikmin are using him (+ the other captains) to ensure the continuation of their species.
The credits take place partway through the game when the first act is resolved, and there is a scene at the end revealing the return of a character from previous games before said character is actually mentioned in the story
While the intital ending after you complete the first main objective can be considered sad, the second ending after you complete the second objective isn't.