Die - Sniper rifle
Only able to hit the head, in another word, the hitscan doesn't register "Until" you hit the head. No more neck or the arm absorbing the rightly placed shot. Also it penetrates players by default. No charging functionality. The damaged is fixed at 75 damage, it allows a custom crosshair where the view is cleaner and slightly wider than having the black background.

Honest act - Medigun
5 kills on players and the uber is guaranteed. Uber lasts 4 seconds. Normal Uber and Kritz can be toggled by Pressing R. The kills are counted either the medic or the patient.

New world - medigun with 3 separated charges. When the charge is ready atleast for one-time use, when the patient is about to die, instead of dying the patient is automatically sent to the nearest teleporter exit with 5% of the max HP, or even 1 hp extinguished (bleeding is kept I don't know). The medigun is charged by nearby teammates dying, or a teammate dying while healed by the medic.

Biblical Bibbidi - Diagnose syringe II
Hitting on the low HP enemy will Diagnose the symptoms and realizing them the debuffs of having the damaged limbs. Slower reloading speed and the movement speed. But I didn't mention the downside other than causing no harm by itself. I'd give another application to this crossbow, When hitting your teammates across the map, I mean 100 hammer units, the teammate heals better from medkits for once. The crossbow projectiles pierces the nearby teammates and has no effects.

Shuttering hopes - Spy's HP faker. Disguise kit or a revolver.
Fake the HP and Blood from attacks initiated by the spy's teammates. Easier to call helps, Pressing The E to catch the medic off-guard would be easier.
If it's a revolver, firing the revolver while disguised instead lowers the indicated HP of the disguised Spy. Not actually lowering the spy's health, it just fakes. Having the revolver while disguised actually aims at himself in the viewmodel. But it doesn't make any gun sounds. Firing the revolver while disguised of course doesn't reveal the spy. Spy's revolver holds 10 or 9 rounds and deals 22% damage of the original revolver.

Option 1, others can hear the revolver while disguised
Option 2, others can't hear the revolver while disguised

Shuttering hopes - Spy's HP faker. Disguise kit or a revolver.
Fake The HP and Blood from attacks initiated by the spy's teammates. Easier to call helps, Pressing The E to catch the medic off-guard would be easier.
If it's a revolver, firing the revolver while disguised instead lowers the indicated HP of the disguised Spy. Not actually lowering the spy's health, it just fakes. Having the revolver while disguised actually aims at himself in the viewmodel. But it doesn't make any gun sounds. Firing the revolver while disguised of course doesn't reveal the spy. Spy's revolver holds 10 rounds and deals 22% damage of the original revolver.

Horse-O-Run WaterThrower
Pyro's primary, His WaterThrower releases the jet of the compressed water. Bullet type damage, very weak damage output. The primary fire continuously knocks back players. Extinguish players. Projectiles are disabled on contact. The wet players are slowed down for 10%, heavy ignores this. M2 grows some giant plants, they emerge from the ground and creates a convenient fence. The fence is teared up by any form of damages, but fire damage destroys them effectively. The damage output is so low it's roughly 30% of the stock flamethrower. Can be used underwater. Accelerates the pyro in the backward direction when submerged.

Lunary - Sniper's drink-then-throw Incendiary pee
First the sniper has to drink some mysterious drink, and his Jarate burns. It takes twice to charge the weapon and it pretty much charges like a gas passer, it doesn't allow the sniper to refill on the cabinet. It has a very weak burning property and the afterburn deals 2 damage per tick. Invisible stickies are sprayed around the landing point. The invisible stickies produce a damaging radius, they produce flame visual effects around them. The damage type is considered "fire". Players trying to cross the flaming border will get damaged. Anyone caught directly into the liquid will get the full afterburn damage of 4 damage per tick. It's the same damage number as the flamethrower. Basically it lays down some stationary flamethrowers. Oils are usually lighter than the urine. The projectile should have less mass than the Jarate but for the sake of the muscle memories and the consistent gameplay experience, the projectile should behave just like the normal Jarate.

Honey Gatheer - Engi's PDA (Or simply Honey Gather)
Teammate's hidden metals are pumped to the dispenser. Engi can't take the ammo from the map. Basically the "Iron Industry" fist weapon I posted awhile. But for all classes, without the buff thing. The max metal for the dispenser is increased slightly, 550 instead of 400. Maybe better sticking to the 400 max.


Scav PDA - engi's PDA
The engi equipped with this PDA can't take the ammo boxes from the map. Metal taken from the dispenser is reduced to half the original amount. It has the exact same system as the above explained, a class based extracting system. But the max ammo capacity is increased to 300. And getting yourself near the dispenser automatically have your metals sucked in the dispenser, and the dispenser pops out small scraps outside. metal over 200 is considered the excess metal thus converted into the small scraps when the dispenser reaches its 400 metal max capacity.

This Hai-Ho thing is an idea I'm circulating for 6 months, but it just doesn't work as it sounds. The ammo box drops per kill, and someone is gonna take it. So an ammo reserve system to begin with doesn't really blend in TF2 except for Engi. And the maps have like a clearly intended engi's nesting spot so, large sized ammo boxes are spawning like a dispenser, there really isn't a place for a dispenser in that regard. People just taking up the ammo and engi losing the opportunity is vastly RNG. Reserving the ammo box in the way for other players is like literally uncontrollable. Yet the weapons try to regulate the engi's effectiveness with the broken metal system. It's either infinite or map-based. So Atleast the engi's metal should be shifted more on, "take the resources from the lost enemy's equipment." Like a scavenger or some shit. Like, seriously. The whole metal thing, doesn't balance out. Engi players just don't realize how much it's RNG to pick up resources from the ground randomly happened to be there because the teammates didn't take it or not. So the dropping metals as a resource should be separated from the usual ammo, in the way it's the same item, extracted for the intended purposes for different classes.

Hai-Ho - Engi's PDA
The teammates nearby taking the ammo box will instead drop a newly created ammo box classified "Scraps", it's basically an ammo box of the equivalent size only obtained by the teammate engis. The ammo box only refills the metal, no ammo for guns are refilled by taking the scraps. If possible it should use a different model instead of the normal box, to identify more clearly. As an engi, taking the normal ammo box will only refill the metal. And the ammo box you took from the ground is replaced with(created instead) an ammo box colored slightly water-ish. The ghost-like metal box can't be taken by the engi, it's available for other teammates to utilize it like any other ammo boxes. The problem with this weapon would be, there will be a lot of unused ammo boxes cluttering around without the purpose.
There is no significant downside other than not being able to refill ammo for his primary or secondaries. A dispenser is able to refill the ammo. Engi players should benefit from this mechanics to start with, though. It's switchable. The down side really is unnecessary though since it's a weapon concept it can't just benefit at it right?

Thermorpho - Spy's throwable sapper
The sapper emits a signal to force sentries aim at the thing. The sapper is indestructible by the sheer amount of the fire the sentry can produce. The mag dump caused by this device drains the ammo rather quickly then just shooting any other targets. The ammo consumed for this target beacon is rated 7 times that of normal conditions. Maybe an adjustment to increase the ammo refilling cost is required as having a dispenser right next to the engi might works out handy. The engi has to get close to the target dummy while trying to not get shot by his own sentry.

Option 1, Sentry still aims at a closer enemy in the higher priority.
Option 2, Sentry is attracted to the throwable sapper regardless of the distance compared to other enemies
- Option 1 is the way go. Because it tests the spy's ability to aim the thing. Also putting the thing too close to the sentry helps out the engi. Easier recovery for the better effectiveness.

Option 1, the sentry doesn't lose the ammo crazy
Option 2, The sentry runs out of ammo quicker than usual
- Option 2 is way far superior to the Option 1 in the ergonomics

Option 1, the sentry's rocket can damage the sentry itself
Option 2, the sentry's self-damaging capability is not active
- Option 1 would be skill-rewarding for the spy.

Option 1, the engi can break the sapper by wrench
Option 2, the engi has to wait until the sapper destructs itself
Option 3, any gunfires can damage the sapper
- Option 1 hands down

Option 1 : The spy has to wait until the currently active sapper is a goner
Option 2 : It's time based until the next sapper is ready and available
- Option 2 would be suited.

Option 1 : Sapper is healed by the nearby dispenser by draining up the metal, and the sapper gets damaged by anything
Option 2 : It's usually indestructible by non-wrench type weapons.
- Option 2, because the option 1 depends too much on the situation and the layout. This weapon alone shouldn't be fixating the engi's overall building routine.

Should the sentry be able to damage the teammate? The answer depends on the minor adjustments. 1, make the sentry emit some sort of visual effects to indicate it's getting exploited. 2, make the targeting beacon very noticeable.

Option 1 : sapper is like a pipe, it rolls randomly. It's not blasted by the rocket's explosion.
Option 2 : it's fixed in the place, like a sticky.
Option 2 is fine.

The best way to use this would be to put this thing right inside the nest, it's important to hit the engi with the rocket salvo. It must be devastating. but again, the engi is supposed to get closer to hit it. So it should be breakable in a hit. Just 1 hit to break to targeting beacon.

About the beacon guided attacks being able to damage other teammates of the engi, bad-teammate dragging down the others syndrome might be annoying. Like, a soldier keeps firing on decent pyros. As much as it's team based, getting teammates exploited and turned into a weapon against themselves is slightly off the fun. So no, the guided attacks shouldn't be able to attack the engi's teammates as it's slightly unfun.