Odorescent (or Odorenaline)
Now a sniper can see the footsteps of a spy after 2 seconds. It could be 2.5 seconds though. The trace spy walked in the past now leaves a transparent marker, the weapon allows the sniper to see the footsteps in the form of highlighted decals.
First, the enemy spies leaving invisible footsteps are server-side, this sniper rifle's scope allows the sniper to see the footsteps. It works for non-transparent spies too, even if the spy is disguised it still can be used to track down the spy. But the footsteps appear after few seconds, the delaying effect is applied for the server-side. It really needs to exhibit the footsteps, colored fogs can be seen on the footsteps alternatively, if colored footsteps alone are not suitable. What I mean by fog is that, surround the places with footsteps with fog-like visual effects so that they could be seen clearly.

Originally posted by Red Mist Suicide:

Daylight Hoax
When spy attacks opponent with this knife, the positions of the 2 players are swapped. But the direction they are facing is kept. Spy has to flip 180 faster than the opponent to stab. Backstab reduces the enemy's max health by 50%. If the enemy is already attacked by this knife, the enemy is marked for "flipped" state, if the enemy is in the "flipped" state the backstab behaves normal and deals 6 times the max health.

The larger classes will get stuck when fighting in a rather confined area. Simply flipping the camera 180 degrees will be too easy for spy to use a bind. So It can be abused. Also the chain stab should be more easy as you move slightly quicker than just walking. Failed backstabs would be more easy to recover.

Signal - Pyro's signal gun
Doesn't ignite people. Automatically explodes after a manually adjusted delay. By pressing M2 you toggle the fuse by 0.1 seconds, minimal of 0.3 seconds to 0.5 seconds. Hitting a target in the head will stun the enemy only at close range. Almost point blank would be blinding if it's a signal grenade. The target can't even flee, it completely stuns the enemy. But a stunned enemy gets a damage resistance only works for the offending pyro. So the usage is limited for ignoring the protector of other light classes. Firstly hit the heavy to pick the medic, evacuate before the heavy regains the control. If there are teammates nearby, the stunning feature would be appreciated by the teammates. Great for poking at light classes by bypassing the other attackers. Also good for stopping mobile flankers for other classes to get the finish move.
Other ways to deal with the delayed fuse implementation would be like. M2 will ignite the projectile not already fired, 0.6 seconds until the explosion. It works much like the loose cannon but the player doesn't have to hold. Simply major the time until the premature detonation. If 0.6 seconds pass before firing the gun, the flash will be expelled forward, resulting in a shotgun like blinding flash. The one caught in the flash will flip the camera 180 automatically. The small mid air explosions have the same properties. Only the direct hit in the head at close range will no-movement-stun lock the enemy.

Recon rifle - Sniper's rifle
Headshot will mark the enemy with "Hey this guy is already shot in the head" Icon. That's it. The downside would be something like "I'm also always marked for death while in a scoped state". The enemy is not dealt with the mini crits damage, they aren't even outlined. But the sniper does, he gets minicrits damage from all sources.

Personal reviews of my own ideas
All-Important Filla - If hitting the limbs specifically is as hard as hitting the head, just immobilizing them will be nothing more than a deserved annoyance. As the debuff requires a medkit to be healed, they will drag out the situation. As such, all medics should be able to see the debuffs as icons on the other player's head. To know who needs the heal despite the health situation.

Standart - The weapon is all about keeping the sniper stand still. It's just too easy to dodge incoming projectiles while charging or aiming the weapon. Moving ever so slightly alone should remove the charge, it really is just a nerf concept but I guess the concept should be focused on keeping the performance regiment level with other contenders. A sniper rifle doesn't have to be on par with the stock since it's arguably one of the best sniper rifle (Of course the best sniper rifle is Bazaar bargain right?). The concept is more about keeping it interesting while applying the debuff to reinforce the intended playstyle.

Chimeratio - This is just fantastic. Powerjack is the meta melee, it gives tremendous mobility to the pyro. Literally the second fastest walking speed class. Removing the powerjack from meta loadout alone would be a good trade off. Pyro really doesn't need a melee, the primary literally is a flamethrower. The weapon clearly reinforces the "staying in the area to progress the objective" playstyle either on attack or defense.

Pyromantica - Pyro's flamethrower. M1 will thrust pyro backward, not so aggressive but still potent. The jet of the gas is concentrated like a fox tail. It's actually a fixed box instead of free moving particles. Reduce fuel by 50%. Taking the ammo box will only refill the ammo by 30%. Defeating an opponent grants the pyro 100% full fuel. The thrust is barely enough to keep the pyro stay afloat, still not enough to 1 to 1 thrust to weight ratio.

Chimeratio - Pyro's bear trap melee II
The original idea of mine just stated it deals 30 damage and slows the enemy, It's melee. The bear trap can be dropped with m2, pyro grabs it like a hand puppet. Hot hand animation can be re purposed for this weapon.
Add bleeding effect for anti-spy, I'm slightly against it but only logical.
Make it make huge noises when someone fell for it, the one caught for it screams too.
The noise of the activated trap is played for the pyro without a difference in the loudness, but there is a distance limit. Pyro will know that someone is caught in the trap as long as Pyro stays in the area. If the pyro walks over the trap, pyro automatically collects the melee, and the melee option will be available again. But right after placing the trap it's not retrievable. I just think bear trap for Pyro feels in-line with the supposed characteristics.

Stand Art- Sniper rifle
The sniper can't shoot the gun while walking, How long you are not moving the mouse charges the weapon. If the player moves the mouse, it consumes the charge depending on how long your mouse traveled (it can be time-based mechanics but flick should negate this so no). Moving the mouse in the velocity slower than the set speed will not consume the charge, the speed in question is very slow. Minor adjustment of the aim will not punish the sniper, flick causes the damage to drop. The charge rate is 60% faster. But the charge will increase the damage only twice, 50 damage will be 100 at the full charge. Walking also consumes the charge.

All-important Filia - Sniper rifle
All body-parts have corresponding functionality thus hitting limbs will immobilize them in the way they make senses. Hitting the arm will disarm them until they get a medkit of any sizes, or it's there until you get healed by a medic. Legs will slow down the target from fleeing. Body is the only component showing no signs of debuff, but headshotting still functions like the stock gun. The gun has a massive damage fall off and the effect is exclusive to close quarter combat, it's to prevent them from being too random as you get less control of where to hit with a smaller target picture. Otherwise hitting the body should penalize the user. Like, everytime the sniper hits the body, they should remove the max health from the sniper himself. Not the target but, the sniper must avoid hitting the body like any other sniper rifle to enjoy the benefits the gun offers.
I came up with the idea like 6 months ago, I think it requires a system level revisiting to make it functionable. Slightly impractical as it can be abused with randomness, it really needs to punish the sniper from hitting the body.

Proper Shield with a pistol - Not really meant for the classes
A weapon for Soldier I guess? A secondary weapon allows you to wield a shield, the shield itself has it's own HP. The soldier is wielding the shield by his left hand, the right arm is for the pistol. If the shield is active, the damage from the frontal side is completely negated. But if you are just having the shield&pistol on the loadout and not wielding it, the soldier gets a complete damage immunity on attacks from his backside. Spy can sap the soldier equipped with the shield regardless of where the shield is on the body. This is to prevent the weapon from becoming the second Razorback, the sapped soldier will be completely stunned for 8 seconds, though immune to the backstab when the shield is on his back. The pistol is just a harassing tool, it should be auto-mag or Desert eagle. He can't reload the pistol, it's limited to one time use only. Taking ammo box won't refil the clip, meaning the player is forced to take the resupply shelf. The shield's HP should be around 80. It increases the knockback from any explosion type damages except his own rockets. The weapon itself reduces the walking movement speed by 15%, if the weapon is currently in use 40% movement speed debuff is applied. The damage of the pistol should be on par with Etranger.

Retreava - Medic's medigun
After the death the medigun lying around will keep the ubercharge, anyone retrieving the weapon will benefit from the pre-existing charge. Therefore the enemies might get the upper hand. Uber removes the overcharge limit for the extensive amount of time.

Spy's revolver - RuBY
Firing from the enemy's behind grants the spy mini-crits. The Damage decreases if the spy is too close to the opponent, regardless of the mini-crits. Because the mini-crit is sorely there to notify if it was from the back or not.

Tick-tack-toe (TTT) - Sniper rifle
When the charge hits 100% the gun itself automatically fires the round, the gun deals 62% more damage than the stock. Without the "auto-fire", left clicking in a zoomed state won't trigger the gun. The scope on this gun is so shiny, it notifies the sniper's position. The charging speed 25% faster. If you fire the gun without the scope, the gun has a tremendous amount of sway. What I mean by sway is, walking, moving the mouse too rapidly, they all affect the gun's current accuracy. They get inaccurate with those elements. Standing still while keeping the crosshair almost still on the same point would retain the original accuracy.

Reminiscent Of The Ancient
Less crude version of the Beggar's bazooka. The design shares the most of the original, but more refined to look like they are factory-made. Soldier loads 3 rounds at once, and fires 3 rounds in a rapid salvo. The gun can hold the clip without automatically releasing it, and 3 degree deviation is removed. But the damage is substantially reduced. Like -70% damage or more.