Spawn of the Green Abyss

One of the many amorphous creatures of the Mythos, the Spawn of the Green Abyss are aquatic by nature, intelligent, and have the ability to hypnotise victims with a song.

In the RPG...

The Spawn of the Green Abyss have higher INT and POW than a Shoggoth, but are otherwise very similar, able to grow pseudopods and sensory organs at will. They are even immune to physical weapons and can regenerate hit-points like one. Otherwise, the primary difference is that these Spawn can sing a song that, if a victim fails an opposed POW roll on, will hypnotise them so that they will obey its every command. An Extreme POW roll can break the trance however, as can a Persuade or Psychoanalysis roll by a companion. An average Investigator only has a 22% chance of resisting this siren song. 

In a video game...

Despite being smaller than a Shoggoth, they are still much bigger than a human, so would be pretty scary to come across. Also, having control taken away from you when hypnotised could add an interesting aspect to the game. Perhaps one player is made to fire upon another, they might not know why this is happening and retaliate in self-defence, possibly even killing their team-mate, unaware that they had a chance of breaking the hypnosis and regaining control.

In a film...

Much like a video game, I think an intelligent Shoggoth with the ability to hypnotise a person could create some unique scenarios, so would probably work within a horror film's plot quite well.