For starters, let me say that I'm not sure if things belongs here or in visual arts, as some of this is definitely about visual arts (and a little is sound design). If this is in the wrong place it should probably be moved, but this seemed the best pick to me.
One thing important to my game's design is making the player acutely aware of the fact that their character is not a badass mega-warrior demigod and the "tactics" that would work for badass mega-warrior demigod characters in other games will NOT work in this game. The game's difficulty falls somewhere between "challenging" and "murderous", if the player doesn't take them seriously the basic enemies and the environment itself can and will brutally murder them. It is extremely important they take the hint as soon as humanly possible. I've got a number of ways to do this already (see below), and I'd like to know if anybody else has some more ideas.
1. The first half hour of the game.
The player character wakes up in a cave, having been brought in the from the sunlight (the sunlight in this world is lethal) by an old man who saw them unconscious in the shade out there. This old man must be over 60 at a bare minimum and is so thin his ribs are visible on his sprite. According to him, he had to drag them inside because he couldn't lift them, and it took him several minutes. He also dies at the end of the conversation. Their story is not off to a pleasant start when they get saved by that guy, getting sick and slightly injured in the process. When the only direction they have in this point is "I.. I live in the broken tower... to the east. You should make your way there, just... stay underground and don't go... through...", that gives them what they need to progress but not enough to feel confidant. What makes it worse is that the way there is blocked by a cave-in, leaving exactly one way to go which is almost certainly the way they were told NOT to go. And sure enough, that path has a paralyzed octogenarian lunatic, a physically and psychologically compromised middle-aged woman, her dead husband hanging from a noose, loose boards with exposed nails, her sickly son, an ankle-punishing pitfall, and a crazy girl whose late father threw her down that hole before he killed himself. And did I mention you don't have a weapon yet? Or any clothes, for that matter? And this is the tutorial, by the way. The rest of the game is MUCH harder. Hopefully, this undignified introduction, their initial injury and the already high difficulty will instill a little caution in them.
EDIT: Small correction, you don't have any clothes at the start of this section. You should have some by the end, depending on your character's size, and the very first merchant in the game is in the next area and happens to be a tailor. (They also give you clothes for free if you aren't wearing any when you first talk to them, and won't do business with you until you put them on.)
2. The player character's species does not inspire confidence.
Three of the five options for player species here is something normally not playable, considered monsters, are ordinarily weaker than player races, and in most games are strictly nameless, one-dimensional mooks serving no purpose but to be slaughtered wholesale by the player. These are orcs, hobgoblins and goblins. Another option is to play as a spinner, which is slightly more unique, but being a gnome with a spider for an arse would still put them in those categories is any other game. Lastly, you can play as a fairy, but they're normally ITEMS, and the few games where they aren't items, they are either guidance characters or extremely weak enemies. There's no choice here that exactly screams "badass mega-warrior demigod PC".
3. The player character is of small stature, to the point where it's actually relevant to gameplay.
The player character is noticeably shorter than equivalent NPCs, and since reach (before bonuses from weapons) is equal to 1/2 your height this creates a noticeable disadvantage. (Though it also makes your hitbox smaller, which balances this out.) Additionally, if they are a hobgoblin or goblin woman, their breasts are a fair bit smaller than those of NPCs, extending 2px instead of 4px. (This does affect their hitbox, reach is adjusted 1px and 2px to compensate.) The difference in stature and reach should serve to make enemies more intimidating, especially when combined with the other things on this list. Below is PC height vs the height of NPCs.
[spoiler]
Orc man: 56px PC, 60px NPC
Orc woman: 56px PC, 60px NPC
Orc boy: 40px PC, 48px NPC
Orc girl: 40px PC 48px NPC
Hobgoblin man: 68px PC, 72px NPC
Hobgoblin woman: 60px PC, 64px NPC
Hobgoblin boy: 44px PC, 52px NPC
Hobgoblin girl: 44px PC, 52px NPC
Goblin man: 50px PC, 52px NPC
Goblin woman: 46px PC, 48px NPC
Goblin boy: 32px PC, 36px NPC
Goblin girl: 32px PC, 36px NPC
Spinner man: 38px PC, 40px NPC
Spinner woman: 42px PC, 44px NPC
Spinner boy: 24px PC, 28px NPC
Spinner girl: 24px PC, 28px NPC
Fairy man: 30px PC, 32px NPC
Fairy woman: 30px PC, 32px NPC
Fairy boy: 20px PC, 22px NPC
Fairy girl: 20px PC, 22px NPC
[/spoiler]
4. The player character's voice is in a higher register.
The game does not have voiced dialogue, but what little of the PC's voice can be heard is higher pitched than that of equivalent NPCs. This, along with #3, is explained by #5.
5. The player character is explicitly stated to be very young.
The player character is much younger than the NPCs they meet in their age group, including their enemies. This is stated explicitly by the first character they meet in the game, the old man that saves them explains saving them at the cost of his own life by telling them he couldn't watch a child die. He then guesses the player's age, either because he thinks they're offended by being called a child, or because he regrets having to leave them alone.
[spoiler]
Orc man: "You look about 14, something like that. It's hard to tell with orcs, since you don't get as tall."
Orc woman: "You look about 14, something like that. It's hard to tell with orcs, since you don't grow boobs."
Orc boy: "Maybe 6? Probably less? I'm sorry, but you'll have to go it alone for a while. I just hope you can manage on your own."
Orc girl: "Maybe 6? Probably less? I'm sorry, but you'll have to go it alone for a while. I just hope you can manage on your own."
Hobgoblin man: "You look about 15, at the oldest. About as old as my great grandson, though I haven't seen him in years."
Hobgoblin woman: "You look about 13, at the oldest. About as old as my great granddaughter was, last I saw her."
Hobgoblin boy: "6, at most? I wish I could do more to help you, but you'll have to fend for yourself. I just hope you can manage."
Hobgoblin girl: "6, at most? I wish I could do more to help you, but you'll have to fend for yourself. I just hope you can manage."
Goblin man: "14, give or take? I don't know, you're the size of a 3rd-grader. How old does that make you?"
Goblin woman: "12, give or take? I don't know, you look like a 1st-grader with boobs. How old does that make you?"
Goblin boy: "5-ish? 4-ish? You're pretty much a baby, it's not right that you have to be here alone. I don't want to leave you here."
Goblin girl: "5-ish? 4-ish? You're pretty much a baby, it's not right that you have to be here alone. I don't want to leave you here."
Spinner man: "12, maybe a little more? Your spider half might be throwing me off."
Spinner woman: "13, maybe a little more? Your spider half might be throwing me off."
Spinner boy: "4 or 5? Something like that. Too young to be here alone, I'm sorry I'm leaving you here, but I don't have a choice."
Spinner girl: "4 or 5? Something like that. Too young to be here alone, I'm sorry I'm leaving you here, but I don't have a choice."
Fairy man: "You can't be much older than 12. At your size, I don't think it really matters."
Fairy woman: "You can't be much older than 12. At your size, I don't think it really matters."
Fairy boy: "4? Maybe a little older? You're so small it's hard to tell, all I know is you're too young. You shouldn't be left alone like this."
Fairy girl: "4? Maybe a little older? You're so small it's hard to tell, all I know is you're too young. You shouldn't be left alone like this."
[/spoiler]
6. The player struggles with strength-related actions.
Nothing ruins the image of being a powerful hero faster than struggling to push, pull or lift something. The player puts a lot of effort into all of the above actions, with the smaller species seriously struggling and often being outright incapable of using certain items, struggling and flailing to no noticeable result. Even a hobgoblin player, despite being the largest and strongest of the available options, puts a lot more effort into these actions than would be required from a human adult, no doubt because of the size difference.
7. The player's animations and sounds.
The player, when idle outside of safe zones, constantly fidgets, looks around nervously, brandishes their weapon or keeps their hands up at chest height, breathes heavily, slouches, occasionally suppresses a whimper or cry, about everything you'd expect of a frightened child in a hostile environment. They do not relax, no matter how long they are left idle, and in fact if left idle for long periods they become more nervous and panicky. Their movement animations are quiet, low to the ground and constantly looking around. When they get into combat, their posture changes and they stand up as tall as possible. Their movements are quick and twitchy, extremely aggressive and very loud, dodging and jumping with with unnecessary stomps to make more noise, grunting on attacks and shouting on power attacks, clearly trying to scare their enemy off. When hit, they scream. They get louder once out of stamina, in and out of combat, breathing heavily with a pained, raspy voice. When low on health, however, they get quieter, choking and sputtering, gasping for air. When crippled, their damaged body parts remain limp, and when idle they will hold and grab at crippled limbs. They also visibly bleed, and will automatically apply pressure to bleeding wounds with idle hands, which does actually reduce the bleeding somewhat.
Their behaviour in safe areas is wildly different, calmer and more relaxed, but even then they still don't stand up straight and only look up from the ground to glance around them every now and then. They are at their best when talking to friendly NPCs, taking up a relaxed posture, but they don't make eye contact much. With unfriendly NPCs, though, they slouch, lean back away from them, keep their head down and look at the NPC's feet. With hostile NPCs, they keep their stance low and their feet wide, eyes locked on them, their hands out in front of them and ready to strike or go for a weapon. While it is unrealistic for this body language to be so universal, it is required for the player to understand it. And what they should be understanding is that their character is a frightened child.
8. The atmosphere of the entire game is claustrophobic and paranoia-inducing.
This is not a horror game, but you'd be forgiven for making that mistake. The game takes place almost entirely in subterranean tunnels and passageways, it's almost always dark and cramped, and when it's open and well lit that tends to be a bad sign. Enemies often stalk or ambush the player, and the game comes with a fog of war and it's a lot closer to the player's back than their front. Sometimes, enemies will even emerge from hiding places in the background or foreground, where they were visible the entire time but likely went unnoticed. There is no music in hostile areas (outside of boss music), so the player constantly hears ambient noises and the sounds of enemies, neither of which is pleasant or comforting.
9. The difficulty itself.
The environments are dangerous, and often include hazards such as flooded tunnels, unstable ceilings, loose or slippery floors, sharp objects and even roots and ledges that will trip you if you sprint into them. The enemies are usually stronger than the player when first encountered, and unlike most players they actually know what they're doing. The game includes a stagger mechanic, crippling and bleed, and enemies will exploit these things for all they're worth. Being killed in this game is very easy, to the point where it's entirely possible to bleed to death from a single knife wound. A lot of the player's bravado will be shot down immediately just from the difficulty, but this is also the reason why it's important they take the hint very early on rather than rushing in blindly and dying horribly ten or twelve times and blaming the game for their own stupidity. (Also known as "The Dark Souls Problem".)
If you have any additional ideas, please let me know.
