Outside the box FPS weapon

[kommando367]

A device that summons a weeping angel or SCP-173 that targets the enemy team.

A 1 time use gun that shoots a projectile that will put a 2m diameter hole in every building and kill everyone (including teammates) in it's path until it reaches that end of the map.

A device that forces an enemy to perform a QTE to tie their shoelaces or they'll trip and fall.

A gun that clouds an area with pitch black darkness and has a night vision scope. Good for knifing people

 

[Captain Pirate]

A gun that shoots a laser-boomerang.
Cuts through anything, including people, and you control it with the analog stick/mouse/whatever, so it's rather badass, however you have to wait for it to come back to the gun before firing again.
You can speed up the boomerang with the right trigger/a key on the keyboard, and this of course makes reloading happen sooner, but makes you less accurate at cutting bitches and hoes due to the speed at which you are directing the laserang.

Second, a gun that takes away one section of scenery/environment, which can do lots of things, such as cause enemies to fall to their death from the lack of platform, or lose cover, or remove armour on a tank, etc.
That same piece can then be placed again somewhere else, for your benefit, such as making a platform, or cover.

 

[Yoshemo]

I like S-Mod's bananas

 

[Aldem]

This might have been done before, but how about a gun which lets you fire three stakes (one at a time, of course) and damages anything within the triangle formed. The farther apart you place the stakes, the less damage you cause. After a certain distance, you wouldn't inflict any damage at all.

 

[Rednog]

Rinoa's limit break comes to mind.
Strapping your dog to your wrist and shooting it at people must take skill and some crazy upper arm strength. I don't think I would consider a propelled dog a normal weapon. Moral implication of you're throwing your dog with enough impact at an enemy to kill them...doesn't the dog get hurt too? Ask your self the question how many more time you can shoot your dog at people before it's skull caves in.

If all else fails you could just rely on this beauty:

Spoiler

 

[TheLastSamurai14]

A gun that neutralizes the targets weak nuclear force

Why not one that removes the strong force?

Fucking vapourise them... NO! ATOMISE THEM... NO! SUB-ATOMISE THEM!

Sounds like the Reality Bomb from Doctor Who...

 

[doomspore98]

A gun that shoots napalm filled puppy robots. The puppy walks up to the enemy, you press a button and the puppy explodes, catching the enemy on fire.

 

[Pegghead]

A hose that shoots glue, so not only could you use it against enemies by sticking them to surfaces/each other/ gluing up the barrel of something like a tank's main gun, but also use it yourself barricade the environment, climb up walls and so on.