These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Goddamned Bats: The fireflies are definitely the most infuriating enemy in the whole game, even moreso than the ghost ants. They don't even attack you — instead they kidnap you, carry you miles away from where you wanted to be, and drop you smack in the middle of a bunch of enemies, usually fire-breathing ants or poisonous roaches. Sometimes they even drop you straight into a pool of toxic ooze!
Nightmare Fuel: The player's small size transforms mundane things like fish, bats and human feet into terrifying menaces. The music is also pretty grim on some levels, namely Level 4 (giant human feet!) and Level 9 (undead ants!).
To say nothing of the spiders that look ugly and scary as hell in levels 4 and 5, and the bees that have the realistic textures and buzzing sound, and don't even get Me started on the bee heads sticking out of the larvae in the beehive levels, ugh.
Not to mention the Fire Ants. No matter if they're throwing spears, chucking rocks, or the kind with wings that fly around breathing fire at you, their faces all look savage and since all the characters including the enemies plastic expressions never change, it makes them all the scarier, and to make matters worse when you kill them you they twitch they're antenna and you can still kind of see their faces which means even after you've defeated them they don't stop being scary, though they're really at their worst in the Anthill level where if you kill them they come back to life as ghosts that continue to attack you, and you're screwed if you aren't near a pipe to flood a room or some lava to trick them to fall into to cause them to get stuck in a loop of dying and coming back to life because you're normal attacks won't work on them at all!
Squick: The sound that the mosquitoes make when they suck Rollie's blood is just... eurgh. Made worse by the fact that they always aim for Rollie's head, so it looks like they're sucking out his brains.