Jar snipe, jar snipe mechanism.
Snipe the piss jar you threw to inflict more people.
Absurdly stolen from Ultrakill.

Originally posted by Bertengkar:

Spy melee : Assiner (Name sake : Ass + sinner + assassin)
Only able to backstab while airborne, grants higher jump while deployed. Disguising as faster classes (include Pyro grabbing powerjack, demoknight forces 0 head state.) adjusts your speed to match the opponent. (no need to deploy the weapon) Excessive speed gained from the knife consumes cloak meter. Jumping while disguised consumes cloak meter too.
The main purpose is to disguise yourself as a scout to get the advantage of faster movement speed. Promote vertical trickstabs by allowing him to jump off people's head more easily. Makes him mobile. But the downside is pretty serious. For those not liking the dead ringer, or being cloaked the whole match.
Minor states ; Negate fall damage for successful backstab.

Added specification : 40% greater jump height when active.
Spy's movement speed perfectly matches the disguised class. When running faster than normal (except discrepancy action or dead ringer's speed boost), consume cloak meter according to the extra velocity. Can't run faster when invisible. Jumping high consumes cloak meter.
Backstab is limited to mid-air, successful backstab negate outcoming fall damage.
40% less cloak duration. Makes a recognizable sound when decloaking,
Picking up ammo box does not refill the cloak meter.

Engi secondary : bio scanner
Non lethal hand-held device. Scan players infront of the user. Doesn't fire anything but the scanner is always on.
It allows people to see the enemy player's health as long as they are getting scanned. It keeps the cloaked spy slightly visible, like someone is colliding with the spy. It has a limited range, only works when crosshair is on the target. When it detects spy, it alerts engineer using the sound and dim light (low-volume, less annoying sounds).

Holoparasite + peracid is the namesake so, Holoperacid (or Holoparacid) is kinda better. Adding for what I said above.

Medic secondary : Holoparasid
Transfer enemy health to teammates, 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. You can zap people while healing one of your teammate. It sucks without moving to frontline, since you can't squeeze the enemy. "Draining" is how I say it but actually it's damage based uber building system. Literally a weak Pyro with a healing capability. Medic doesn't heal himself from doing them, non of them.

Ideas that doesn't work.
Cuti-E sniperrifle (Cringe pun of QTE) : As you scope, the meter drains rapidly. But the meter starts from full. Meters only affect headshot damage. Bodyshot damage is fixed. Problem is that it's absurdly OP without adding downsides. It's only valuable for those who can quickscope, so adding "anti-bodyshot" stuff won't restrict much. Since they aim the head to start with.

Spy secondary : Mann Magnum (I don't know)
Revolver that requires reloading of individual rounds. Shotgun style functioning.
Beside that, it's a straight forward variant of the default revolver. I personally find the default revolver's reload to be a bit quick, it actually gives spy unnecessary DPS. I want to promote hit and run tactics of spy more. Trades longer reload for higher burst damage. Slower firerate for demanding of skills.
Stats be like
-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.)

Scout melee : Foamer grounder (Foam + former + baseball pun)
A soft baseball bat with jigglebone. Right clicking reflects projectiles.
Basically a sandman without the ball, but the ball is either rockets or pipes.
It's actually just a miniscule airblast. 50% Explosive damage vulnerability on wearer (while deploying it). It's just a hit-or-miss concept of a weapon. deals less damage than the default bat (around 70% less). Useful utility for dealing with the long range rocket spam.
Of course it comes with a long cool down for each swing.

Oh, I forgot to mention their health cap recovers over time. (Like I said about GRU)
The soldier weapon above I mentioned is actually a reference to Davis gun, a recoilless rifle that shoots a countermass to counteract the forward thrust. So that they don't have the iconic funnel shaped gas expansion nozzle. Anyway it was off-topic.

Soldier primarily : The Unalterable piercers
Reduce 35% of max health on hit, dies instantly when the opponent's max health reaches 0. Only way to recover this is to have a medic overhealing you. Thinking about running gloves mechanism, it's likely possible to implement such features in the game.
They shoot a solid projectile, it's a non-explosive type weapon. They have 300% faster projectile compared to the original rocket launcher, exactly the same with Directhit to avoid confusing yourself with the muscle memory. It performs higher jump(in a similar fashion with the jetpack) by clicking m2. The backblast launches you, it doesn't fire the round. Instead, they are ejected from the rear side of the gun, and the projectile lay around. It consumes 2 rounds per jump. You are only able to jump twice without reloading.
The visual is 2 thin iron tubes welded together to form a sort of the twin barreled anti-aircraft gun feeling. It utilizes the default reloading animation without visualizing the sabot shells.