You know who are the scariest people to deal with? The ones who hide weapons or magic powers inside their own bodies. That's just plain wrong.

Or it could just be ritual tattooing.

Share a story about someone's weapons or abilities, that were literally made a part of them.

One of the characters I played was a Scurrilian, which basically meant a human sized mutated crab.

One of the big pro's this race had, was the fact that they had 2 massive pincers, which I could control aside from my arms, and basically had their own turn of combat. It basically gave me an extra attack round.
In a system where two attacks per round was already quite good and if you spend your points right you could make that easily a 4 attacks per round thing.

It's not exactly a hidden weapon, but it is part of it's body...

Basically your character functions like ganzack from the devil's tower arc.

Man, Pathfinder Alchemists are all about this kind of wrongness.

My current low-level alchemist has a scorpion familiar...that's actually a specially sculpted tumor made from his own flesh. It can attach or detach to his arm at will.

It's actually pretty neat. Besides the +4 to initiative, it also has the protector template, meaning I can split damage between it and me...and while it's attached to me it has fast healing 5. Not to mention I can send out my tumor scorpion as a scout whenever I need one. And from a flavor perspective, it REALLY weirds everyone out.

Other alchemist discoveries include things like grafting on wings, extra arms, tentacles, a whole parasitic twin, turning your blood into poison, mummifying yourself, etc. All kinds of fun.

I don't think I've ever played a cyberpunk game where at least one player hasn't had some sort of weapon installed. From the basic and easily hidden (like vampire fangs and razor blades fingernails) to the showy and impractical (implanted chainsaw in forearm, detachable grenade fingers) all the way to the downright scary (detachable brain case that can swap bodies. In a heavily armed and armored wheelchair. With his old flesh cadaver preserved and riding on top. Not even exaggerating.)

My personal favourite was a one shot where we rolled randomly for our augments. Myself and another player character were in pvp, dueling with monowire whips concealed under fingernails. When they tangled due to a fumble, I was close enough to shoot him with the dart gun I had concealed in my left cybereye. Unfortunately, the biotoxin took a turn before it impacted him, and he gutted me with a set of claws straight out of an X-Men comic.

Of course most of those systems have some sort of cyberpsychosis or other sanity loss mechanic just to emphasise how weaponizing your own body makes you less empathetic and less human. Not that that has ever stopped a player from wanting a flamethrower attachment for his kneecap.

In a space-opera/sci-fi/cthulu-ish horror campaign. My character needed extensive skin surgery after a small accident involving a hellgate on a space elevator.

As part of that I decided to not only have her skin upgraded as armour, but to instal acid spray containers in her forearms, with exits in the palm of her hands.

Sadly, the campaign didn't quite last long enough for it to come in handy.

Every tattooed monk ever.

One of my first Scion characters had a series of tattoos on his arms that acted as a relic. While it never happened I would occasionally get worried that we'd run into someone who would decide to rip off his arms to keep him from using the powers they gave.

One of the foes my players had to face was a copy of the mind of an ancient and insane wizard which had taken control of a peasant girl. He wanted to free the soul of the original, which the player had trapped inside a dwarven artifact by pure chance, but had no magical powers he could use and feared above everything being captured to have information forced out of him about his long term plans. So what he did before attacking the player was to hide a magical bomb inside the body of the girl, setting it to explode after a certain amount of time. The player captured him, found out about the bomb and did their best to save the girl, but failed. That was the point where they started to seriously hate this villain.

One of the foes my players had to face was a copy of the mind of an ancient and insane wizard which had taken control of a peasant girl. He wanted to free the soul of the original, which the player had trapped inside a dwarven artifact by pure chance, but had no magical powers he could use and feared above everything being captured to have information forced out of him about his long term plans. So what he did before attacking the player was to hide a magical bomb inside the body of the girl, setting it to explode after a certain amount of time. The player captured him, found out about the bomb and did their best to save the girl, but failed. That was the point where they started to seriously hate this villain.

As a GM for the game Scion I made an NPC based on Marrow from X-Men. She was a servant of the Titan of Time and used her own body as her weapon in the literal sense. She splintered her bones and pulled them out from under her skin as knives. If the story had ever gotten farther, she would have been pulling out longer bones for swords and larger implements or even pulling her own spine to use as a whip (or cudgel, if her skull remained attached). Her powers were focused around the healing Purview, so she was regenerating the lost bones and even able to shift her flesh and organs as needed to pull out whatever weapon she was making.

This also made it impossible to disarm her. They could take her knives, and she could walk through a metal detector with no problem, then pull a bone out if a fight started.

I remember back in the old Planescape: Torment game when magic tatoos were more than just a thing, they were as valuable as any armor piece. (more than literally, as the Nameless One couldn't wear any armor). And they came all on little flaps of skin that you could stick on and peel off. Tatoo parlors had whole human skins on racks showing their artistry. Good times.

Had a guy once, wanted to make a grappler. Monk didn't work out for him, so went through a whole bunch of sourcebooks, came out with a Barbarian/Warshaper/Primeval (from Frostburn; used a Dire Bear)/Fist of the Forest (Complete Champion; among other things, adds Con bonus to AC). Even if he couldn't grapple, he could manufacture and augment his existing natural attacks and get a lot of them. Took some sort of feat that gave him powerful build, DM ruled it also applied to his alternate form; DM also ruled that unarmed attack (from FoF) counted as weapon, so could give up a claw attack in exchange for full attack unarmed plus all his naturals as secondaries.

One minute, a buff hobo in at bearskin and loincloth, the next a bear nearly as big as an elephant with elastic limb that's immune to crits, stuns, and with Steadfast Determination, a constant Prot v. Evil item, good luck getting him with Fort or Will saves; even if he rolled a one on a Will, he had a 1/day reroll a save item. And since Con boosted both his HP and his AC, even if you could hit the guy you weren't gonna kill him.

He could only shift about half an hour a day all told, he was pretty solid even in normal form, and death on four legs in bear form. Even after the player left for school and we decided a glorious death was the way to go for the character, the DM basically had to cheat to get rid of the guy.

Don't remember exactly since it was long ago, but in one session we faced a guy who had severals damned soul sealed in his SCARS. covered in deeps scars from neck to toe, and could summon the ghost-like things out of theses scars. they had various painful effects, painful for us, that is.