Turn the light + Instant cloak
Cloak watch that allows the spy to instantly turn invisible.
When invisible, the foot steps gets 1.3 times louder for spy.
While cloaked, the max HP keeps getting reduced.
There is no damage compensation.
When decloaking, Magician's smokes are out. The Bop sound effect with the released smoke makes it easy to spot.
The cloak meter refils so quickly that it's full in 3 seconds. But one cloak lasts 2 seconds max. Reduces the primary damage for 15%.

Engi electro shotgun.
When you hit m2, the last projectile stays in the air. When 2 airborne projectiles are nearby, they create a line of a thunderbolt. This electro beam damages the enemy in contact. The projectile stays in the air for 1 second. Holds 6 rounds, the slag projectile deals bad damage. The projectile velocity is the same as rescue ranger, the max distance between the projectiles is 3 meter in a human term, it's hard to tell 3 meter in the TF2 gameworld. I'm imagining 1.7 times the medic's height. Supposedly 1.6 times. The electrified damage is dealt 50~60, the projectile itself is 25~30 damage. The projectiles pierce through enemies indefinitely. The mid air projectile has damage even when stationary. It's basically playing with marbles. The friendly engi's projectiles don't connect. When more than 3 rounds are up in the air, they only connect with 1 another projectile in a firing order.

spitsar
The pipe deals mini crits and donk sound&visual effect when the shell is hitting the target at angle narrower than 60 degree from vertical. The pipe has a stable trajectory with much heavier projectile. When the shell hits collision at vertical angle narrower than 60 degree, the shell explodes regardless of if it's a wall or a floor. The shell holds 6 rounds. and it phase through roofs, while phasing through roofs, the round gets invisible until the altitude is lower than the then previous roof. I don't know if detecting roofs only is consistently enough when implemented with practically available resources.
The explosion radius is 30% of the original grenade launcher. Reload speed is 50% faster. non-detonated projectiles disappear. The damage dealt by this weapon has no knockback. The projectile doesn't randomly rotate mid air. When looking down at an angle below horizon, firing the weapon discharges all the loaded ammo. These released projectiles on the floor explode immediately and likely killing the demoman. The rounds fired this way does not travel sideways, and falls straight downward. This could be exploited by standing on a pointy high ground. Might be better just deleting the rounds fired downward. The weapon is supposed to be fired upward like a mortar. Might be better giving an increased damage against demoman himself, but it could make him launch himself further, which is not that desirable. Maybe added crits damage against himself, when it's a crits. If it deals knockback against demoman himself. It could be used as a tool to maneuver. Might be too much of a utility, otherwise demoman has to empty his clip to 1 or 2 rounds. I expect it easily, that demo starts dumping his mag to nothing, just to perform a pipe jump. It could be a part of a useful gimmick though.

spitsar
The pipe deals mini crits and donk sound&visual effect when the shell is hitting the target at angle narrower than 60 degree from vertical. The pipe has a stable trajectory with much heavier projectile. When the shell hits collision at vertical angle narrower than 60 degree, the shell explodes regardless of if it's a wall or a floor. The shell holds 6 rounds. and it phase through roofs, while phasing through roofs, the round gets invisible until the altitude is lower than the then previous roof. I don't know if detecting roofs only is consistently enough when implemented with practically available resources.
The explosion radius is 30% of the original grenade launcher. Reload speed is 50% faster. non-detonated projectiles disappear. The damage dealt by this weapon has no knockback. The projectile doesn't randomly rotate mid air. When looking down at an angle below 90 degree, firing the weapon discharge all the projectiles. This released projectile on the floor explodes immediately and likely killing the demoman. This could be exploited by standing on a pointy high ground. Might be better just deleting the rounds fired downward. The weapon is supposed to be fired upward like a mortar.

Detonator with the headshot registration.
Temporarily blinds a player like a flash, around 2 seconds on hit. When detonated mid air like a detonator, it causes the enemy player inside the radius to get ignited for full duration afterburn at 2 damage per 0.5 seconds, no mini crits against burning player. And deals no damage by the explosion itself. Hold 3 rounds, reload at once.

Face stabber, headshot knife. That's it. But the effect is temporal blindness, for around 3 seconds. But the medic with a medigun can cure the patient quickly, shortening the duration to 1.2 seconds with a stock.

spitsar
The pipe deals mini crits and donk sound&visual effect when the shell is hitting the target at angle narrower than 60 degree from vertical. The pipe has a stable trajectory with much heavier projectile. When the shell hits collision at vertical angle narrower than 60 degree, the shell explodes regardless of if it's a wall or a floor. The shell holds 6 rounds. and it phase through roofs, while phasing through roofs, the round gets invisible until the altitude is lower than the than previous roof. I don't know if detecting roofs only is consistently enough when implemented with practically available resources.

If the long projectile spawns at the muzzle, the damage is dealt for the players behind the engi. And the visual disorientation would be noticeable. So the projectile should be made invisible for a short period of time, and the damage registration should be deactivated too. Longer the projectile, More it takes for the projectile to appear. But the lag could be problematic. So a placeholder projectile should be created first, and the activation of the longer projectile should diminish the temporarily laser. Or else it could be made so that the muzzle's location move forward, which I question the validity of such implementation. The weapon holds 6 rounds, the weapon could be made in a way to just have 6 template stages for each projectile length.

Prototype Pomson 5164th
or Pumpson
Reloads 75% slower. Holds 6 rounds.
More charge you have, the projectile gets longer. And the damage increases. Penetrates enemies, does not multi-hit the same target.
Repeatedly shooting without maintaining the high charge results in a lowered performance.
Kind of like a compressed air gun. The longer projectile's speed is the same, the velocity change just messes up aim prediction, instead, the projectile's length combined with the relatively slow velocity allows for a more unique movement strategies for the enemies.

Doddering measures, a character attacked by this weapon mid air slams into the ground and gets damaged. The downside would be a a shorter hit detection range. And the reduced damage, -30% damage would.