Emergency Button
Spy cloak or engineer secondary, look like the good old red button

(+) on activation : throw your really fast in the air (z velocity 3000)
(+) activate parachute on use
(+) remove all malus on you
(+) reload your primary
(-) need full metal (50 min to activate) or full cloak
(-) you will be stuck in air for a while...

Just a weird idea I get after trying stuff like that for my ff2

Decoy Sapper
Sapper for spy

(+) when removed : explode and deal 50 dmg to everything in a small radius
(-) sapper fizzle after 5 seconde
(-) when removed (or when it fake kill the sentry) the sentry recover the health
(-) -50% sapper health
(-) special particle

When a invincible nest... With a camping wrench spamming Engi is godlike, go punish him !

Portable Warhead

(+/-) projectile gain speed over time (from 50% to 150% projectile speed)
(+/-) projectile gain blast radius over time (from -50% to +25% at long range)
(+) 75% lower damage falloff
(+) on kill reload 1 rocket
(-) -50% clip size
(-) -25% reload rate

Smoke Bomb
Cloak for spy

(+) dead ringer cloak type
(+) 75% chance to dodge attack while cloaked
(-) disguise smoke while invisible
(-) consum 85% of the cloak on activation

Ultimate protection in last resort, sell your invisibility to get a mini-ubercharge

Initiator (my names suck... Ikr)
Shield for demoman

(+) increase charge duration as health go down, (+1 second every 30 HP missing)
(+) bash damage increased on distance (up to 150% tide turner bash dmg)
(+) on bash, turn 50% of the damage into health
(-) no charge control
(-) almost no bash damage at close range
(-) -50% base charge duration

Danger Cannon
Sniper rifle

(+/-) increase charge rate as your health go down (up to +100%)
But decrease charge rate as your health goes up (down to -50%)
(+) increase damage by 25% when under 50% health
(+) on kill : +25 HP
(-) no headshoot while not fully charged

Alchimist Sting
Saw for medic

(+) on hit : apply ONE of these effect

• 25% chance to jarate for 5 second
  
• 25% chance to mad milk for 5 second
  
• 25% chance to bleed for 5 second
  
• 25% chance to ignite for 5 second

(+) on hit : reset all malus duration of the victim
(-) -25% damage
(-) -25% attack rate
(-) no random crit

Barbed Barbarian Bomb
Sticky bomb for demoman

(+) on hit : make the victim bleed for 3 second
(+) +50% blast radius
(+) no damage falloff
(+/-) special activation mode (scottish resistance)
(-) huge noise on activation
(-) on activation, the explosion have a 0.75 second extra delay
(-) -75% damage against bleeding target
(-) -25% attack rate

Typically the type of sticky who make you scream "Oh Sh!t"
Can't one shoot, putting 2 sticky is stupid, but this can take down a scout in 2 separated explosion

Electro Magnetic Eggs (rework of the old kaboom stick)
Grenade launcher for demoman

(o) use sticky jumper grenade
(o) grenade are always crit, but deal 75% less damage (just for the aspect of the grenade)
(+) +100% blast radius
(+) disable buildings for 3 second
(-) 50% longer fuse duration
(-) -50% clip size
(-) -25% attack rate & reload rate

The aspect of the grenade is important due to her different gameplay
It always deal 75 damage in a large zone due to crit, but is harder to land properly, this need a ambush gameplay

Carpet bomb
Grenade launcher for demoman

(+/-) auto fire full clip at once (like beggar, but instantly)
(+) +3 spread angle penalty
(+/-) each grenade have a random fuse time between -25% and +25%
(+) grenade have a low bounce & roll
(+) on kill increase clip size
(+) +50% damage for grenade that hit surface
(-) don't explode on direct hit
(-) -50% damage
(-) -25% blast radius
(-) no random crit

To explain it easly

(+) press fire to load grenade, release to unleash a carpet of grenade
(+) kill increase clip size
(-) grenade don't explode on direct hit and deal low dmg on direct hit
(-) -25% blast radius
(-) no random crits

This suit the concept of the Demoman, using this defensivly to lock a zone with explosion