One-Shot Pistol
You don't have to make a fancy model, just reskin a default gun to white. It only has one bullet. It does enough damage to instakill if it hits the head, but it is inaccurate at anything longer than medium range due to the spread the bullet has. Bodyshots do 25 damage.
Killing a bot, vehicle, or player with it will regain a bullet. If you have no bullets left, attempting to fire will instead perform a(somewhat weak) melee attack.
Blaster Launcher
Purple reskinned Rocket Launcher that fires a rocket you can control. You fire it, a rocket pops out, you control the rocket by moving the camera. Medium-high damage, fairly large-ish explosion.