The Shotgun is one of the least powerful weapons in the game in the game, capable of killing noenemies with only a single shot, even from close up.
Most players consider them to be the weapon to never take. Although they are not the most powerful ranged weapon you can get (actually the worst), unlike the Scepter and the Plasma Cannon they are much harder to find early in the game and are practically risk-free to use.
They can be found in several places. They may be sold in weapon shops, and also have a low chance of being found inside a crate.
All Shopkeepers carry shotguns to enforce order in their stores, but you will have to fight them for it and will be branded a criminal by doing so.
A guaranteed shotgun can be found in a Restless Dead level, buried under a unique grave with 'ASH' inscribed upon it - a reference to the protagonist of the Evil Dead movies.
Functionality
The shotgun fires scatter shots, discharging 6 pellets simultaneously that each deal 1 point of damage.
The pellets are fired on slightly divergent trajectories and spread slightly as they travel, but this doesn't really affect long range accuracy.
There is a short reloading time between shots, but the weapon has unlimited ammunition.
Most enemies will be killed with a single shot, but large, tough monsters can withstand several hits. Some enemies are immune to gunfire, including the Ghost, Olmec, Croc Men and Bacteria. The Black Knight's Shield will reflect your bullets back at you, but he will be vulnerable if you can make him drop it by stomping on him.
Remember that the recoil from firing a shotgun will throw you back by a whole tile. Always make sure that this won't cause you to fall off ledges or push you into a trap.
It's also a good idea to try to ascertain where your shots will land, as stray bullets could hit Damsels, Scarabs or Shopkeepers off-screen.
The light produced by the muzzle flash can be used to get your bearings in dark levels.
It is possible to jump one tile higher while carrying the shotgun by pressing jump and the attack button at the same time, its even possible in mid-air or with the spring shoes on (for a total of 2 tiles higher), this definitely makes the shotgun an interesting platforming tool.