Giant shoggoth

Giant Shoggoth
Giant shoggoths are one of the most powerful monsters in SLASH'EM, although not necessarily the most dangerous. They have a speed of 20 (making them faster than 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'll be walking around with corroded wands and keys for a while).They also have a very high level, meaning lots and lots of HP.

Fortunately, they aren't whirly like, say, air elementals, and thus wands of digging will work...if you have one.

The shoggoths and their giant variant don't actually pose a threat 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.

The problem is that shoggoths are considered a valid polymorphable form. This means that a chameleon can turn into one on dungeon level 9 (it could have been a polymorph trap, too), and, since the shoggoth is faster than the player, it will almost certainly kill him.

(This information was found on http://alt.org/nethack/dudley/?314 and posted here for convenience. This page will also need touching up)

Encyclopedia Entry
"... 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 ..." [ The Thing on the Doorstep, by H.P. Lovecraft ]

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 ... [ At the Mountains of Madness, by H.P. Lovecraft ]