Onslaught (my gzdoom standalone game/TC) has a lot of unique weapons in it. Here are a list of the most unique ones in the game. Later on I will post info on the monsters. Many of these are from the original game design document from 1995. They have been updated to use sprites from the beastiary and in some cases are straight from there but the idea is the same, at least!

Plasma Pistol
Bastards unique sidearm fires energy bolts rather than bullets.

Lever Action Shotgun:
A terminator 2 inspired shotgun.

Double Shotgun:
A semi auto double shotgun, more powerful than the default one in doom 2 and if you tap the fire button you can fire it faster.

SMG:
A High tech Submachinegun

Assault Rifle :
Standard CSC Assault Rifle Weapon:

Auto Shotgun:
A full auto shotgun, very OP

Laser Rifle:
A more powerful version of the plasma pistol

LG80:
An Experimental homing bullet battle rifle

Flamethrower:
A flamethrower

Spread Rifle:
An experimental Bullet weapon that fires multiple bullets in a spread, sort of like an OP shotgun

Nailbomb:
Thrown like a grenade these explode and send nails flying everywhere

Napalm Cannon:
Shoots a spread of burning projectiles

Triple Barrel Chaingun:
3 Barreled Chaingun that is very OP and fires spread attacks like a shotgun, only minigun speed

Rocket Chaingun:
A chaingun that fires missiles

Asskicker:
Dual Rocket Launchers mounted on Bastards trusty backpack

Sniper Rifle:
Useful for long range combat but besides that not so good
Enemies in the game range from cult soldiers to robots to insanely OP mutants. Some of them are rather new in terms of when they were conceived, others are as old as the original design in 1995

Cult Guard
A cult guard that guards lightly guarded areas. Armed with a SMG and Cloaking Shield

Cult Soldier:
The Standard Cult infantry, armed with an assault rifle.

Transylvanian Horror:
A mutant that is the weakest you will fight

Vampire Mutant:
A stronger kind of mutant armed with homing fireballs

Musclehead:
A strong mutant with a melee attack that does tons of damage

Lardass:
A huge fat mutant armed with energy weapons or explosives, depending on the variety

Blasphemous One:
A huge flying head armed with spread fireball attacks and lightning blasts
Viper Cyborg:
A half man half machine warrior armed with nailguns and nailbombs

Super Mech:
A super Powerful flying mech piloted by a cult soldier

Fear Elemental:
A super powerful mutant that shoots super deadly area of attack attacks

Stranglevine:
A powerful vine like enemy that shoots tons of projectiles at you

Cultist:
A cult member armed with a powerful hellish railgun