Genela Genela - Pyro's flamethrower
Liquid nitrogen dispenser, lives up to its name. The frozen enemies gain 300% resistance to all damage types, but melee crits on them. Meaning you deal normal amount of damage to the frozen enemies. What frozen state means is that, it gets them multiple separate debuffs at the same time. They can't turn their head like in demo's charging restriction, they slow down significantly. But not completely immobile. 5 seconds they can't move. Once they are thaw out they get anti frozen buff for 10 seconds. Pyro use this to bypass enemies to pick one enemy. Once this is done, Pyro must run away or there is not much Pyro can do. Because they get damage resistance, and anyone is forced to attack frozen enemies with melee, they have to get close to the one. But if the frozen enemies are many, getting to the core is pretty risky. It shouldn't be spammed.
It takes few good seconds to freeze an enemy completely, it slows enemies slowly though. Not instantly freezing them until the buffs and debuffs (Reload speed, firing speed, camera speed, again walking speed, all adjusted at once instead of liner.) start kicking in. The crystal thrower(visual) itself deals decent damage. Opposite team's actual flamethrower can remove all the effects by simply spraying M1. They can instantly unfreeze anyone.
There is a lot of way to trap the frozen enemies, like stickies or snipers. But the point is, being frozen is about getting preserved. 500% resistance gained from being frozen and only melee bypassing this is pretty balanced. And 5 seconds, the number isn't much, Sure, it might be too strong if there are snipers or demo, but what else. Not much.

Diamond Shaker - Soldier's melee

Hitting anywhere drops a small ammo box for a chance of 25%. The usage is when you are getting healed by the dispenser, you use this to drop an ammo box. Assuming you are already maxed out on the ammo. The engi can utilize the ammo to further expand the buildings.
Super fast swing, 150% attack speed. 90% damage penalty. It takes forever to deal sufficient damages. But you look like Steve.

Ringading - Scout's Scattergun
Variable barrel length if it's possible even. The more you deal damage, the barrel gets longer.
Meaning your pellets concentrate.
Or If you it might be depending on the remaining ammo count. If your remaining ammo is low, the pellets group up tight. So that your potential DPS increases only if the user can aim decently. It demands less skill maybe. Because the point of shotgun is to aim the center of the body not about hitting without actually looking at the target. More pellets to land, you easily get more DPS from tight grouping pellets.
It's a dirty joke anyway. What about getting damaged, would that S H R I N K the barrel length? The method is kind of like Baby face's blaster. It's better being "reduced over time".

Fume - Pyro's flamethrower, or a smoke thrower.
Spread smokes only the enemies can't see through. Only your teammates can see through the smoke, they are visualized as slightly transparent haze. So that your teammates are actually aware of the blinding curtain's existence. It lasts very short, shortly after it's deployment the smoke starts to phase out. The decent usage is to cover an engi under construction. Or to simply help others escape from the enemy fire. A very supportive weapon, fitting for Pyro. But what if it dealt less damage, it would be more cool. I think it should have like 75% raw damage reduced and let's say, no afterburn. 25% damage of the original, do note, it's hard to see him if you are literally inside the smoke. But again, make the smoke as thick as possible for both pyro and enemies. No exploits to bypass the visual, or else. Pyro shouldn't be able to see the enemies too, and airblast should remove the smoke instantly. Both enemy and the user. Pyro himself not being able to see the target is a requirement for this weapon.

Hellframe - Pyro's flare
Crits against enemies launched airborne by the airblast.
No crits from burning targets, if they are flying the story is different though. This thing simply replaces the situation when the thing crits. Pyro really need to get close to do this, so it's just worse. Normal flare can crits if they are that close. So... what would be a good upside for it. Something to fuse with, whatever.
OK, Blast them away. Like a very strong knockback. Maybe cause an explosion only if you hit the right target, and make the explosion's effect exclusive to the one launched above. If they are launched above like a "second airblast", it's easier to switch to the main weapon and airblast again. So that it can be a good combo weapon.

Mannizer (Cool name)
Sniper rifle that fires extremely fast projectile bullet, flare style tracer effects.
Bad for people with bad network connections. It's fun because you have to take account of the bullet drop-off to snipe enemies in the distance. This is the best way to nerf sniper rifles in any circumstances. It's just a concept for one weapon, though. The point is that it's more fun to use than a hitscan. Real life guns have a slight delay for the bullet to land, bullet falls off vertically. The effect is negligible in close quarters combat. So what about the snipers, I think this idea is pretty good. About the possible delay, the huntsman exist. What about using the huntsman's head registration instead of the smaller one for the hitscan. It will compensate but it might be too much, and might aswell negate the whole point of shooting slightly above them.

Bear trap for pyro's melee.
He grabs it like a puppet and moves it as if a mouth.
Alt fire places the bear trap on the ground.
It deals 30 damage and slows enemy for 3 or 5 seconds.

Legion rock II
The old idea was to restrict enemy player's ability to pick up nearby resources, when placed on the ground. I'd make it able to place up to 5 at the same time, instead of 5 reserves. Also I'd make it able to remove only by wrench and pyro's certain melee. So that an engineer is tasked to move up like a plumber, it would be cool if multiple engies did what their independent roles correspond to. Having 2 engies helping eachother has too much synergy and makes it better than 4 non-supportive engies. So one engie goes for removing the sapper and one can just stay in the nest. More or less the idea forces engies to leave the nest for even other spies with normal sappers.

Kind of a joke weapon - Parrot
Soldier's rocket is replaced with a miniature plane, the plane(rocket) itself fires the forward facing machine gun. But it might be better firing downward, like Delightning rocket launcher. Plane doesn't crash but phase through objects, because it might be used for offensive jokes.
Only loads 1 round in the clip, the weapons resembles a catapult or even an aircraft carrier.

Delightning's alt-fire should affect the oldest projectile only, one by one in the order you fired. The Apolloximate and Authority were (kind of) the same weapon untile I refined it now. When I was bathing 4 months before, I forgot the idea and I was suffering from it. I now remembered it with a shock. Probably because I got a notification of Ultrakill update (Sorry for it being completely off-topic, I really am sorry,) It can be fused together to be mild. But these 2 ideas can be 2 weapons instead of too much stats on a weapon. What do you think? I can't find the mid point.

Apolloximate Soldier's rocket launcher
Rocket detects "airborne" enemies nearby, and detonates if it gets closer enough. So without having an enemy in the air, it's just a rocket launcher. the point is to launch them airborne, and you are easier to intercept enemies. Side effect is that, it detonates too early making them explode at the tip of the radius, resulting in a far less lethality than manually guiding them right. But it's just easier to damage them at least, better than a complete hit or miss I guess. Adds +15% fire rate at the same time -30% reload speed.

Self-claimed Authority - soldier's rocket launcher.
The explosion causes enemy to fly vertically without dealing damage. Directly hitting the enemy results in them losing the ability to control mid-air. The target flying because of this weapon can be damaged by the direct airshot from the player, granting a critical hit. The damage itself is lowered by 20%. It has a limited range, if the projectile exceeds the limit, the rocket explodes mid air without damage. The explosion caused by this limit won't have the effect of sending the targets flying. Against yourself the weapon works like a rocket jumper. But it can launch enemies airborne by hitting them too. It's simply a practical version of rocket jumper, but the rocket jumper was never competitive anyway. Added range limitation is to keep the user from harassing enemies from far away, the airshot is only consistently done in a close range, so it shouldn't be abused at a longer range. It's nearly that of a melee, but the ability to stun lock enemy by directly hitting them, the ability to launch yourself without hurting. The ability to actually cause damages, The ability to control the crowds. It's not any better than the pyro's airblast anyway. By saying "sent them flying" I mean, it's completely vertical, no side-way motion. It's supposed to be predictable.