PDA that changes the level 3 sentry's rocket salvo to a heat-seeking homing missile, as they prefer "hot" targets. Pyro is always at the highest priority. They are attracted to Pyros like a magnet. So that a pyro can theoretically disable the sentry's rockets. Pyro usually sucks against sentries, so this might be interesting. They are hard to dodge but easy to reflect. Only thing to be careful is that amplify the tracking capability only for pyros so that it can punish bad pyros for not using his alt.

PDA that enhances the sentry's detection range 20%, but reduce max ammo capacity for the sentry by 70%. And reduce the metal storage of the dispenser by 50%.

PDA that turns your buildings to a blood sucking succubus, If you stay close to your buildings, the buildings automatically start sucking your health to restore themselves. You transfer your health as a metal equivalent. The downside is the visible instability you get.

review
The Unalterable piercers : A rocket launcher that apply the state "Capping the enemy health by 35% per hit, removed overtime but the current HP doesn't not restore.". It takes 2 rounds to fly like a jetpack with the backblast, pierce up to 5 targets(Include your teammates, does not deal damages.). 300% faster projectile, shoots solid AP rounds. Doesn't really work against light classes, just an anti-pocket weapon. If the heavy is getting overhealed, it still removes 100 max health, It requires 5 shots for the equivalent of 500 damages. So there aren't many reasons to not use direct hit over this weapon.

A new weapon concept : High-octane
Sniper rifle that is capable of charging even longer, the damage gained is dealt to the sniper too. The maxed out body shot deals 200 damage, the sniper takes 50 damage from shooting the rifle. If you shoot the sniperrifle at 140 damage, you don't get damaged. If you shoot a 151 damage shot, 1 damage is dealt. The headshot still deals the bodyshot damage to the sniper himself.

A review for the weapons I imagined.

The paper : You can ignore the medic holding the non-damaging melee at all, you can keep attacking other classes, but the medic might survive because of it. That's the concept. But actually, no. You'll end up getting targeted more, because the attacker will try to kill you before you get to land a melee first. Pyro will just airblast you into oblivion, landing a melee is actually pretty hard by itself. Most players will just ignore the effect and try to pick you anyway, thinking it a good trade. So whatever you think the medic will just die in any opportunity.
(100% reduced damage. Upon hitting the enemy, mark the enemy with "convention" state.
If you are the one marked for it, killing the medic results in losing your ability to attack for 7 seconds.

Assiner : The technique here is that you can have something like revolver to jump, then switch to this knife. So that you don't overshoot yourself. You can perform normal jump and still get the stab as you switch your weapon early enough. Picking up ammo not charging the meter prevents the spy from reaching the front line faster. Only good for skilled players, the one using it thinks he is cool but never helping his teammates. Not practical.
(Spy melee | Backstab is limited to mid-air, successful backstab negate outcoming fall damage. 40% greater jump height when the weapon is active. Spy's movement speed perfectly matches the disguised class. When running faster than normal (except discrepancy action or dead ringer's speed boost) consumes cloak meter according to the extra velocity. Can't run faster when invisible. Jumping high consumes cloak meter. 40% less cloak duration. Picking up ammo box does not refill the cloak meter.

Holoparacid : Damage rate not enough to actually contribute the fight. Always forced to stay close to the enemy. Good for supplementing a worse teammate. As you die quickly, good thing you don't have to charge up to 100% to be vailable.
(Second beam tracks enemy to damage them. Damages done is converted into Uber meter. Normally healing teammates consumes Uber meter. Doesn't really have Uber to pop. Healing without the remaining charge is possible but it works less efficient. M1 heals teammates and M2 drain from enemy players. Medic equipped with this can target 2 players at once. Drain beam contrasted with purple glow. It's a damage based uber building system. Medic doesn't heal himself from damaging the target.

Mann Magnum : Why not.
(-17% clip size (6 rounds to 5 rounds) | 20% damage bonus | -10% fire rate | Reloads each round individually. (first insertion of ammo takes slightly longer due to the necessity of extra animation.)

Foamer grounder : The opposing soldier shoots the ground at close range, demo will have a tough time but he can just spam, there is no way to deny a sticky with this thing. One swing is just not enough.
(scout melee with jiggle bone. Alt-fire reflect projectiles. It's Airblast with the visual effect replaced with Sandman alt. 50% explosive damage vulnerability on wearer after failing to reflect atleast one projectile at time. -70% damage. It takes sooo long to refill the alt.)

Bio scanner : Shit, it's garbage without the additional "Anyone's sentry can attack the revealed spy" stat. There is nothing to gain from knowing the opponent's current HP. Scanning invis spy to reveal them for a puny amount of time is something a stock pistol can do, since you have to track them with the precise aim. The better stat is that you don't have to reload, but hell. Alerting other teammate with a siren is something you can do with the voice command.

Waver : Lucks good man. Nobody cares about the meter, they will use it for gambling. It might be fun, though. Still better than something like "As you scope, the meter is drained rapidly. But the meter starts from full. Meter only affects headshot damage. Bodyshot damage is fixed."

U.F.P : You might think it's not a good complement for Frontier Justice, but no. It's really good used in conjunction with the Frontier Justice. The crits are not always available, the ammo capacity is what holding back the gun's capability and reliability. Using it as a combo weapon actually conserve the ammo. If you have crits to start with, you don't have to worry about 1 vs 1 situation anyway. You might struggle to have someone just right in the place, so hitting the throwable directly stun lock the target for one good second, but it takes the exact second to have the frisbee perpendicular to you, so that as you are ready to boost your shots, the enemy starts moving freely again.

Jettison and Cryor is kinda similar but they suggest completely different playstyle.
Jettison's flames remain only like 5 seconds, they stick to the surface (since they are invis-stickies producing flame visual effects and a damaging zone around it.). They can't be affected by the airblast in the way hostile stickies do, they don't roll around. Only the airblasted area combust(detonate). Cryor on the other hand, non-damaging gas remains 15 seconds onward. The gas inflicts 0 damage by itself, all connected gas(chunks) starts changing into something we call fire. They are affected by the extra velocity given by the airblast.
Jettison is like the impression we get from meet the team trailer. A building surrounded by the fire is something we don't see in the game.

Meet hook is a lesser kunai that forces spy to play a proper spy. I said it's the max health of the enemy but it's the current health referred. It's not unfair, spy can inspect anyone's health. Once meet hook is used, the knife is unusable until you manually release it by clicking the left mouse button. I'm sure most players wait until the shield breaks eventually. It just forces spy to be a kamikaze unit afterall, very little chance to escape the enemy territory. But I think it's cool to walk away backward, shooting the revolver in the slightest amount of hope that it might kill the enemy chasing after you.

Cumburst and jar snipe is just, just good.

Double action : Ultrakill

Renten marker : I think it should be 7 seconds. The game should notify players injected with it.

Stressman : Simply amazing play-wise but in total nothing is gained.

Kelpy : You can't play it like a caber, because your HP is just not enough for doing it. It's more like a Quickiebomb launcher but 2 times quirky. It's mean't to be played defensively as a support-line artillery, since you can't defend yourself with just 2 stickies loaded at the time. If you stickyjump with it, you fly far better because you get more damage from it. There is no sticky delay preventing you from bombing yourself like a detonator. If you are overhealed you might be able to pull off mid-air jump, otherwise you are probably dead.

Scrampnel : So hard to use, there is not much to reward you. I question why I came up with the stat. It's way better being a simple shrapnel-based pipe launcher for a primary slot. Like, "extended range" shotgun or something?

Immolation cream : meme, a cheap demoknight with no self-sustainable capability.

Legion rock : Crappy sapper for good teammates (and bad spy).

DareD : Thinking it takes 300 damages to fill the meter, you really don't get the full benefit out of it. Players end up looking like a dumbass after emptying the whole clip, "can't cancel the reload animation" is a good way to balance this weapon. I think the players in the same team might be better being able to see an invis scout.

Incendiary airblast concept weapon : Good for a combo, but you better finish them without the flamethrower. Pyro deploys it slower than the stock, this one holsters faster though. The stats slightly enforce you to approach the enemy while wielding the flamethrower. But it's never enough to directly cause damage. To finish classes with health less than 175hp, you need to airblast projectiles to damage them first. Otherwise a single flare is not helpful. Fixed 90 damage still leaves a room for enemies to counter attack you. You need the skill to airblast enemy projectiles at close range, or you don't get to finish them off. Afterburn damage is insignificant, it is just a good uber-farming material. It relies too much on the projectile-based classes hostile players are playing.
I think this is waaaay better than the current Degreaser, The Degreaser's 1.5 damage per second overwrites any other 6 damage per second afterburn. This weapon might be too favorable for those only use the default flare to deal damages. In my mind, pyro is never a close-range combat class, they are specifically categorized as "Middle ranged fighter". Pyro's flame out-range shotguns, If the pyro is too close to the enemy with a shotgun, the pyro gets as much damage as they deal. The way pyro really works is that the airblast fucks up the opponent's aim so bad that you have an open-window for the flares to fuck up targets even more. One thing to note here is the flare. The flare deals fixed 90 damage, it's really hard to exceed over 70 damage using a shotgun, because all shotguns have a huge fall off. A good pyro never stays too close to the target, they want to reflect the projectiles. Try getting closer next time, they might airblast you to take a distance, or they will retreat while facing you. That's because they are pressing W just to compensate your S. That's the truth. So, this weapon I really want in game. Standing next to a pyro is advantageous if you are brave enough to endure the consistent DPS. If the pyro airblast you, the pyro actually stops attacking you for a moment. Pyro's forward movement is way faster than most other classes if they are walking backward. Just stop looking at the pyro chasing after you and face the direction you are heading. Balancing pyro's weapons must be based around this principle of letting it be a "middle ranged weapon that actually sucks at extreme close range". I might be confusing a pyro with demo's I think...? If I want a balance, that's the best scenario. A refined demo with a different utility.

Pyro's flamethrower : (Incendiary airblast concept)
M1 flames deal 70% less damage
Airblasted opponents get ignited for full afterburn
Airblasted projectiles inflict burn damage, functions similarly to the Cow mangler's alt-fire.
20% faster holster time
30% slower deploying time

Pyro's secondary : Immolation cream
Cover himself up with a bucket full of napalm. You become a fire coated walking unusual, or an unusual itself. Takes 2 self-damage per second. Disable all healing sources. Taking small ammo boxes speed you up. Or it might be better changed to "Killing enemy grants speed boost until you die (Stacks up)". Enemy takes massive damage from colliding with you, direct contact with the enemy inflict maximum afterburn. The empty bucket is still there and you can have it. Taunt requires a partner to start, pyro hugs the partner using both arms. If it's done under the condition, it insta-kills enemy. Pyro used this item revert to none-cosmetics state for obvious reasons. (You know the water waders's texutre glitching up, something like that.) The pyro turns into a muddy monster, it resembles a magma.

Spy's sapper : Legion rock
Throws a small rock that disable the nearby enemies ability to pick up resources, ability to repair buildings. Works for medkits & ammo boxes, dispenser. Spy has an infinite amount of the weapon. But it has a charge meter for it to be reusable. It can be destroyed with a simple gunfire. The weapon comes with different styles and you can cycle it pressing the manually assigned reload key. It destroys itself in 30 seconds. Still long enough for something that might be placed somewhere unreachable. For the purpose, it produces noises just to make us locate it.

Scout's primary : DareD
Namesake of Dardick revolver pistol. Stores 3 rounds only. The gun itself is made of glass(transparent metal btw). Successful shots provide a cloaked reload. Scout can't shoot while reloading, can't reload until the clip is empty. Can't switch weapons while reloading. The cloak meter is damage based, it's automatically consumed on the reload. Reloads each round lever-action style. Duration of cloak at full is equivalent of reloading 3 shells. If the cloak meter runs out, scout keeps reloading uncloaked. Dardick pistol's cylinders look like an atomic sign too.

Demoman secondary : Kelpy
Scottish resistance mk.ii, only able to load 2 rounds. Precisely aiming the mid-air sticky to detonate makes the explosion bigger and slightly enhance the damage. 40% more self-damage. Sticky delay is removed, meaning you can hold right click and still perform the "aiming down" thing. You don't have to set the crosshair on the projectile to explode them, they just enhance the base-functionality of the sticky launcher.

Demoman secondary : Scrampnel
shoots pill-like projectiles, they land vertically. They are their own launcher and right-clicking activates them one by one in the order you placed. The projectiles hop upward and spray shotgun like hitscan downward at the height above mercs. The shell deals mini crits on heads. 8th sticky always crits, overwriting the older sticky still keeps the "7th" sticky crits, and the new one is crits again. You can just keep adding new stickies and they all are crits essentially. Only the small explosion at the top is crits boosted, the shrapnel is still normal or mini-crits based on the body parts the shell land. Airblast disorientate the direction the sticky itself is facing, they no longer count as an active sticky. Though, they don't really have the direction to hop, they just get launched "Above". Airblast can affect the projectile launched from the ground. The second shell still land on the pyro somehow, mostly becuase their end is facing the pyro.
About the graphics. You remember the hopper mine from HL series?, now replace the thing with upward facing pipe bombs and call it a sticky.

Pyro primary : Cryor
Spray the gas, build up the gas in the same place to charge up. press M2 to combust the gas and launch the flame to far away. Basically a less complicated dragon's fury. The gas itself has the same property as the green gas from the gas passer. But I'd add extra property. As you dip yourself to the gas, the wet effect stacks up over time and the next burn state gets extra afterburn damage and duration. Not only m2 functions as an ignition starter, they are like normal airblast. The downside is a visible lack of kill-insurance.

Medic's melee : Stressmann
As long as you are healing someone, 35 percent of the damage done to you is dealt to the one you are healing instead. Except any self-constrained damage. 10% damage vulnerability on wearer (non-active). Excessive damage against the remaining HP does not count. Examples are backstab, headshot, alike. If someone backstab a full health medic, 62 damage is transferred to the client. If someone backstab a medic with only 30 hp, the damage dealt to the client is somewhere around 11.

Meet hook's corpse slows the spy carrying it. Cloak consumption is doubled.

Medic's primary syringe gun : Renten marker
Crossbow like property of healing a teammate, heals until whopping full. After 14 seconds they loose all the HP of amount you healed with it. Any healing source overwrite the amount of rent. The client has to heal in the duration or they are again low health.

Engineer secondary weapon : U.F.P (Unknown Flying Pancake)
Frisbee you can shoot down yourself to turn your penetrated shots into mini crits.
Frisbees turn 90 degree on flight and stay afloat in the air for 5 seconds. When the frisbee is perpendicular to the trajectory, the frisbee stops and is at 0 velocity. You can hold them up to 5 frisbees. You regain them only from dispenser and a resupply shelf.
Idea: Stackable minicrits, x1.8 damage is too much so multiple minicrits are now double-mini and it multiply the damage 1.7 times for once. Making the layers of the frisbees to boost your primary weapon's long range viability works.
Directly hitting a target with frisbee stun lock the enemy for 1 second.
Says makin' bacon everytime you kill someone with it.

Pyro's flamethrower : Jettison
the flames remain on the walls and the ground for like 4-6 seconds. The flamethrower's range is severely limited, 60% shorter than the stock. Airblasting combusts the remaining fuel on the ground and extinguish, for a trade of burst damage. Support weapon for playing the objective, doesn't really reinforce WM1 playstyle. Good for defending chokes.
The weapon shoots invisible stickies that have a continuous burn damage radius, at the same time they shoot shorter range version of normal flame particles. The airblast actually detonates the invisible stickies with a flame visual effect. Of course they don't deal as much damage as actual stickies but they are way smaller and more like particles. As for the explosion, they are envisioned as flames.

Spy's melee : meet hook
The backstabbed enemy becomes a meat shield until the shield's HP is 0. Blocks all damages from the front. The shield's HP is determined by the enemy's max health at the time they are killed. They explodes at 0hp and spread their gore.

Scout's mad milk gimmick : C** burst
Shooting your mad milk with the primary now grants bleeding damage for the same radius. Bleeding and milk is a strong combo already so, it sounds good to me.

spy's revolver : Double action
Hold left click until the hammer is cocked, releasing it shoots the weapon.
Headshots are registered as mini-crits. Down side is the delay, no actual base damage buff. mini crits aren't that good too.

Sniper's primary weapon : Waver
The charge meter swings back and forth, a player has to shoot at the maximum point.