Positive, but rare, and conditional, effects in natural language and with in-world fairytale logic rather than plusses, bonuses and re-rolls. This gives players a reason to record them and makes them easier to remember.
(For most people, D&D being what it is there are probably people who find it easier to remember that they have a +3 on a conditional re-roll rather than that they can bleed apple seeds from a wound.)
The idea here being that a particular situation comes up and the player says 'ahhh, but I carry a Troll Tooth scar so I get to do *this*, or *this* should happen.
And the DM says, 'but where is this scar and what does it look like?'
Player - 'well its *here* and it looks like *this* and I got it in *this* adventure when we did the thing. Remember that?
Conditions for Getting a Scar
It shouldn't be too easy, or people will game it. So;
- It needs to make sense in the described event; "The Troll bites deep into your forearm and bears you to the ground" or "The Goblin Scimitar carves a chunk out of your cheek and nocks the bone, your head flies back." Not just; "They swing and hit."
- There should be some exceptional success on the opponents part, or exceptional fail on the players part, as related through dice results. A crit by the monster, being reduced to 0 HP, an unusual magical or physical effect, being tied up and tortured, or a fumble from the player.
- It's largely the players choice as to whether they get a *Scar*, with a mechanical effect, or just a scar. If someone gets covered in dragonfire then they are going to be scarred up but they shouldn't have to accept the complex rules elements of a dragon-breath scar unless they want to.
- The player can decide where on their body it is, broadly. It has to make sense with the imagined sequence of events.
- Once a player does accept a scar, it’s not easy to get rid of. It should be possible, but requiring high level magic or a situational quest.
- Why doesn't magic heal it? In the case of magical beings, it may be their effects can't be fully removed by healing magic. Divine or other magical healing means that the body can only heal in relationship with the spiritual or magical state of the whole. So, in pseudo-Eastern philosophy, a scar from a particular event can't heal because your Chi is knotted around it, and this relates to your spirit and psychology as well as your flesh. Maybe you subconsciously want that scar because you need to remember that event. In western philosophy, maybe you need to remember the sin, perhaps your humours are altered around it or whatever.
Point being, if you accept this idea, it should be known in your world that there are some scars, both natural and unnatural, that won't heal, or that need special, magical or mental changes to be allowed to heal.
THE SCARS THEMSELVES
First, standard, boring, non-material scars from creatures that aren't specifically magical or poisonous.
ORCS, GNOLLS, BARBARIANS, all those 'Proud Warrior Race' guys.
Scars from these beings are non-magical, but get you serious cred in other Orc and Barbarian communities. Those guys just sit around comparing scars all day anyway, it’s their written language.
You get a chance to engage if you are willing to bear your chest and go "Do you speak so, to the slayer of SNARLGUT?!?!?!. I shall tell you the tale of our battle, for it was MIGHTY INDEED." This could turn a combat/monster encounter into a social/but-probably-still-combat encounter.
Appearance - Practically probably just a normal scar.
Maybe a green tinge from Orcs who lick their blades before battle (Orcs have anti-coagulant saliva? Makes sense).
Barbarians tend to use serrated blades which, in reality probably aren't always that different in their effects but in fiction can be said to leave saw-tooth tears.
Gnolls can tell which Gnoll bit you, simply by the patterning of teeth, which they recognise. This could be good because it shows you either killed them or just met them and survived, indicating that you are worthy of respect. (Or that you are not that tasty).
They key thing with a Dragon being that just surviving is impressive, prevailing even more so.
Claws and Teeth
These are heavy-duty versions of Quints speech from Jaws. Even an idiot should be able to hold a bar or a group of rogues spellbound with the story of how that happened. Start thinking of some cool shit to say and bust it out whenever you need to impress a random human encounter or raise your cred with a prospective employer or hire. Assume that whenever you are describing the story of your dragon-scar in a social environment you can at least hold a crowd, if not persuade them.
Burns and Breath
Partial immunity to the effect is the most interesting possibility. That doesn't really make sense if the effect is a blast furnace, but it could make magical or poetic sense.
The most 'useful' parts to get scarred are the hands, so you can grab stuff in fire or acid, and the torso, so you can avoid critical/lethal damage. So if you want a useful hand or torso burn scar you should have to take a hideous facial scar as well, that massively disadvantages you socially.
People with real burn scars do sometimes get them tattooed to reclaim them, so if you get the right magical tattooing added to your Dragon scar then you should get full immunity, for that particular part. (Meaning that when the Dragon toasts the rest of you that one bit is left as a magical relic for others to nab.)
Gas Scarring to the lungs could mean that you heave and wheeze continually, and maybe occasionally cough out poison gas, but you can also breathe that gas without difficulty.
The Ahab Effect
Limb loss or massive facial scarring means you no longer suffer a fear effect from that particular Dragon, and it’s easy for you to persuade others to fight it, but you have Ahab RAAAAAAGE whenever you think about it and just can't let that shit go, you are effectively geas'd to go after it.
Goblin scars grow tiny multicoloured mushrooms and sometimes leak a colourful pus if poked or massaged.
Those little mushrooms make the consumer laugh uncontrollably, they are also quite nutritious so eat them yourself and giggle or drug others to distract them.
Licking your own pus lets you have Goblin thoughts, and act in Goblin ways, you get sneaky and crafty, can find places to hide and can make traps and strange devices. The DM has to tell you if there is any place to hide that you missed and you can contort yourself to fit into small spaces. Just hope no-one hears you giggling like a loon in there.
Appearance - Goblin scars heal in the shape of grinning mouths, no matter the original cause, so if you fight Goblins enough you end up covered by these fungal smiles.
DEEEMONS (& DEVILS)
Demon Scars resolve into black letters in an infernal language. The power of the words increases with the power of the Demon that caused them. Very high-powered demons are able to track you with the scar because they have ETERNAL HATRED for you now.
Such a scar can even be passed onto descendants since Demons are timeless.
'Holy' creatures and Paladins and whatever are able to read it and see that you kicked a Demons ass, or at least survived it.
'Lesser' Demons and supernatural creatures become scared if they see it, reading out the words will frighten them.
The words get you access to certain places, magical portals or altered states.
So yeah, you got scarred by a Demon and that’s 'bad', like a curse or whatever, especially as in regards to the particular Demon. But, the rest of the time it’s actually, effectively, cool as fuck since you carry all the badassery of being 'Demon Touched', meaning you get invited to all the cool parties and can wear sunglasses indoors, but none of the negative social effects since 'good' people know you beat up Demons.
Sure it hurts a bit when you enter a church, but you can always tell attractive members of your preferred gender "Yeah, sure was tough when I fought that Demon and sent it back to Hell, got its mark on me now. A curse, some say, [rueful sigh, sardonic smile] I guess that's just the card's you're dealt when you are a PROFESSIONAL DEMON FIGHTER."
Each Ghost is so unique (or should be, in a good game) that the scar should help connect you to the conditions of their creation. It throbs in the presence of their murderer.
The scar helps find your way around places that person was familiar with. Like the dim body-memory you have of where you are in your house or locality, the way you can find your way home drunk.
If you get drunk you get flashes of the Ghosts memories, maybe if you sleep you dream of its death.
If it’s dark, and its quiet, and you don't seem massively out of place and act like a dick, other ghosts will mistake you for one of them, part of their own memoryscape, and you can talk to them about what’s going on with them.
If you set the Ghost to rest the Ghost-Scar becomes a Ghost-Trap, you can force damaged or befuddled Ghosts into it. Good news; they are out of the way and they can't hurt *you*, directly. Bad news; they tend to pop out when you are having nightmares and fuck about with stuff nearby. Arguably-Good-News, people really don't want to go near you when you are sleeping.
Appearance - Just a shade off your natural skin tone in daylight, but silvery and reflective in moonlight and pale in darkness.
These help detect the presence of that particular races technology or tools.
They also move around the body at will and always point the way to nearby portals to other dimensions or whatever.
They usually itch when that particular kind of creature, or its effects are near. So you can check if Mind-Flayers are near, but also if anyone nearby has also been effected by them, like a secret brain-slave maybe?
Appearance - Fucking weiiiiird. Not like scars at all. Continually rippling bits of flesh, always mutating slightly on a basic level, different in shape, texture, colour and feel each day.
(They might be like Teratomas actually, but probably players wouldn't want to keep track of those.)
Ray Scars, from a Beholder or anything like it, would look more like modern industrial laser scarring than anything medieval. Just a straight burn across your body
Petrification - You now have stone or ceramic fingernails, or stone teeth, or one stone finger that works like a real finger.
Disintegrate - You got transparent X-Ray flesh where that ray landed now. Plus your bones inside look like blue glass. That's not actually that useful but pretty cool nonetheless.
Fear - A howling munch-scream medusa-head burnmark with the path of the head-snakes following the path of the Ray. Creatures that cause fear are actually nonplussed by seeing this in full and can't activate their effect for a round.
Death Ray - Not only is this scar classic 50's nuclear-phosphorescent, but the sweat from it is also phosphorescent. If you collect enough sweat and use it to mark a portal or forehead, that thing is briefly warded against death magic. (Also people want your sweat now).
Anti-Magic Ray - If you rub something against this scar and it actually is magic, the scar will sting a little. These scars are always negative-image colour to the rest of your body, like they are in a different dimension.