"The Coming of the White Worm"

by Clark Ashton Smith
originally published Stirring Science Stories, April, 1941

Evagh, a sorceror of Hyperborea, finds himself in a sticky situation, when his tower and the surrounding village are taken by a strange magic which freezes everything, and everyone.  Said magic emeges from a colossal floating iceberg which has sailed into the harbor.

Evagh is taken aboard the iceberg, which serves as the ship and home of a creature called Rlim Shaikorth, and six other powerful sorcerors, who have been abducted by RS and had their bodies now magically altered so that they can survive in RS's inhospitable environment.  In addition to sparing their lives, RS has promised them all the gift of mighty magical wisdom and knowledge.  In exchange for obeisance.

Oh, and did I mention that RS is a bit, gloopy white worm-thing?

Soon after, Evagh notices the number of his companions dwindling one-by-one.  He learns also that the magics that have altered him to allow him to live in RS's environment have made it impossible to live in earth's.  

So they sail around, freezing and destroying the world Evagh knew, while the RS's guests keep disappearing and he keeps getting bigger and fatter.

One day, Evagh finds himself alone, and RS asleep.  The voices of his vanished comrades inform him that, while RS has eaten both their bodies and their souls, their consciousness is active and can speak, while RS is asleep.  They tell him how to kill RS (which is pretty straightforward), but that doing so will cost Evagh his life as well.

Evagh hacks RS with his sword.  RS splits open and a seemingly endless supply of black gloop pours out of him, apparently drowning Evagh and destroying the floating iceberg-ship.

Weird stuff, man.  This sinister fairy tale from C.A.S.  is a favorite of some, but I don't consider it one of his most memorable (I first read it 30 years ago and couldn't remember a blessed thing about it, while there are other Smith stories I remember vividly).  An interesting oddity all the same, and Smith does Smith better than any of his imitators.