Shoggoths and giant shoggoths are among the most powerful monsters in SLASH'EM, although not necessarily the most dangerous. Both forms have very damaging attacks, move quickly, and have an acidic engulfing attack.
Shoggoths also appear in dNetHack, with properties very different from the SLASH'EM creatures.
The standard shoggoth is an unpleasant monster to encounter. It is faster than an unhasted player and can deal a substantial amount of damage, all while degrading every iron and copper item in your inventory. This includes non-weapon items as well, although the effect on those is mostly cosmetic. Fortunately, like its larger cousin, it prefers to hide rather than fight, and so can be left alone.
Giant shoggoths are more powerful versions of regular shoggoths. They have a speed of 20 (making them as fast as a player in speed boots), an engulfing attack which, in addition to doing a ton of acid damage, corrodes most of the corrodable items in your inventory (which means you will be walking around with corroded wands and keys for a while), in addition to two very powerful claw attacks. They also have a very high base level, meaning lots and lots of HP.
They can also teleport when they flee. However, they will not teleport to encounter you, preferring to remain hidden. If you choose to reverse genocide them, you should do so on a non-teleport level; otherwise they will soon scatter themselves.
Luckily for those who encounter them, shoggoths are not whirly like air elementals, and thus a wand of digging will work to expel you and set them to one hit point. However, an engulfed player still has to deal with their 8d10 engulfing damage at least once, not to mention their bite and corrosion attacks. If you have low HP, it is best to avoid being engulfed altogether. Acid resistance, as granted by a lab coat, alchemy smock, or yellow dragon scale mail, will protect you against the damage from the engulfing attack but not from the biting attacks.
Also, shoggoths, unlike other super-monsters in SLASH'EM, are not immune to death rays. Given the greater number of charges on wands in SLASH'EM, an awake and non-hiding giant shoggoth (see below) is well worth a charge or two from a wand of death, or a casting of finger of death. A wand of death is also a good option if you find yourself engulfed and lack a wand of digging, or if you are low on hit points, as the shoggoth may re-engulf you before you can respond if you zap it from inside with a wand of digging.
The shoggoths and their giant variant do not actually pose a threat to a careful player when they normally appear, because, like trappers and rock piercers, they hide until you enter their square. Thus if you have warning or extrinsic telepathy, you will never be taken by surprise by a "natural" shoggoth. And you will, by the time shoggoths can appear. This is probably a very good thing because Demogorgon's lair is full of shoggoths, which would almost be as bad as Demogorgon himself if they weren't avoidable in this fashion.
Unfortunately for some unlucky players, shoggoths are considered a valid polymorphable form. This means that a chameleon can turn into one on dungeon level 9, or any monster could theoretically step on a polymorph trap and turn into one. Since shoggoths are faster than the player, this is very likely to become YAAD.
The fact that shoggoths are considered a valid polymorphable form is very useful for any player with polymorph control and a source of polymorph. As a giant shoggoth, you will wipe out shopkeepers in the early game, but more importantly, the form can be used to rob the black market later on. They have enough hitpoints to weather One-eyed Sam's attacks, and since they are not @'s (and have no heads anyway), they need not worry about the beheading and canceling abilities of Thiefbane. Being immune to stoning, they do not need to worry about the cockatrices that guard the black market, and the other monsters there are quite trivial. Giant shoggoths do not make particularly good traveling polymorph forms though, as they are blind, cannot use weapons and armor, and have no hands. Monks are better able to make use of the giant shoggoth form, as the Eyes of the Overworld will allow sight, and doors can be dealt with by casting force bolt. However, you still will not be able to access containers in this form, so it is still better suited to situations where you need a strong melee form (such as the Temple of Moloch or the Astral Plane) rather than a general-purpose travel form.
Another use of giant shoggoths (but not the normal variety) is that their corpses are capable of conveying teleport control, but also teleportitis. This is not terribly useful in and of itself, as typically one will encounter them only shortly before getting the Amulet of Yendor, which in SLASH'EM prevents all forms of teleportation. However, a careful player may find it useful to reverse genocide them, provided they use some permanently engraved and well-placed Elbereth squares. They have a higher chance than tengu to grant the intrinsic, and they always leave corpses. In addition, their corpses are also capable of granting poison resistance, shock resistance, and cold resistance. They do have a high nutritional value, so a player would be well-advised to use a tinning kit or amulet of magical breathing when doing this.
Shoggoths would appear to make good pets, as they have extremely damaging attacks and move quickly. Shoggoths are also relatively easy to tame, as the regular variant only has MR 25 and will grow up into a giant shoggoth. Because they tend to hide, it is very safe and easy to walk up to one and repeatedly cast charm monster until it becomes tame. While shoggoths are certainly capable of doing large amounts of damage, the fact that they hide, eat both metallic items and regular food, and always have a chance of turning traitor mean that they are difficult to control, especially without a magic whistle. Despite having extremely powerful attacks, even giant shoggoths only hit monsters as a +0 weapon, meaning that they are completely incapable of damaging many of the more powerful monsters that you will encounter in SLASH'EM. Their only advantage over a Solar is that they are much easier to tame and it is easier to raise their tameness, as they will eat almost anything.
(Much of this information was adapted from http://alt.org/nethack/dudley/?314 and posted here for convenience.)
In dNetHack, the shoggoth has a unique suction attack with a variety of effects. Each effect is independent, and more than one can occur with the same hit. The effects occur in the following order:
- If your HP is at less than 10%, you have a head, and you aren't wearing a helmet, there is a 5% chance of your head being sucked off, killing you. No further effects will be applied this turn.
- You are slowed by 6 movement points per hit.
- There is a 10% chance that both your legs are badly injured.
- There is a 15% chance that your weapon is sucked out of your grasp. High strength can help prevent this.
- There is a 10% chance that your boots are sucked off, unless they are buckled boots.
- There is a 15% chance that your gloves are sucked off, unless you are wielding a weapon. High strength can block this completely.
- There is a 7% chance that your shield is sucked off. High strength can help prevent this.
- There is a 25% chance that your helmet is sucked off.
Shoggoths come from the works of H.P. Lovecraft. The encyclopedia entries are excerpts from Lovecraft's works.
They appear as massive amoeboid creatures made out of iridescent black slime, with multiple eyes floating on the surface. An average Shoggoth measured 4.5 meters (15 feet) across when a sphere, but they can get much larger. They show signs of intelligence.
"... in the place of utter blasphemy, the unholy pit where
the black realm begins and the watcher guards the gate -
I saw a shoggoth - it changed shape ..."
It was a terrible, indescribable thing vaster than any subway
train -- a shapeless congeries of protoplasmic bubbles, faintly
self-luminous, and with myriads of temporary eyes forming and
un-forming as pustules of greenish light all over the tunnel-
filling front that bore down upon us, crushing the frantic
penguins and slithering over the glistening floor that it and
its kind had swept so evilly free of all litter. Still came
that eldritch, mocking cry -- "Tekeli-li! Tekeli-li!" and at
last we remembered that the demoniac Shoggoths - given life,
thought, and plastic organ patterns solely by the Old Ones ...