Spawn of Hastur

Octopoidal, aquatic creatures with unspeakably hideous faces that dwell in the foul and murky lake of Hali with their sire, Hastur. Like him, they may be summoned to Earth, but only when Aldebaran is in the sky.

In the RPG...

The Spawn of Hastur used to have 10-point armour, which made them pretty much immune to bullets, but in the 7e Malleus Monstrorum, this has been reduced to 6 points. Of note, they are one of the few creatures that can swim, crawl, and fly, though they are more adept at the former, with only a 4 Move on land. 

    The Spawn's tentacles used to have an 84% chance of killing an average Investigator outright, but this has since been neutered considerably, and even at the maximum, now only deal 9 damage. They do, however, have a maneuver whereby their victim is swallowed whole, resulting in instant death. In the old edition, death was instantaneous, but in the new one, death is now delayed until the 4th round, presumably so the victim at least has a chance of escaping. This can be achieved by either an Extreme STR roll or an opposed DEX. For an average Investigator, the chances of each are 10% or 25% respectively, so they should definitely opt for the latter.

    Further changes made for the 7e Malleus Monstrorum include decreasing the attack chance. I believe this is the first time I've come across this. From what I've seen, attack chances are normally increased. They must have thought 75% was just a little too high. STR, DEX, and POW have all been altered as well, with STR decreasing, DEX increasing, and POW keeping the same average but having its range reduced.

In a video game...

Cthulhu is the only other creature in the Malleus Monstrorum that can swim and fly, so in that regard, the Spawn of Hastur are fairly unique, so would probably be a worthwhile addition. The only catch would be their reliance on Aldebaran being in the sky, but I'm sure that could be worked in.

In a film...

I'm remiss to say that I don't actually know much about Carcosa, and Hali, and the like, so I couldn't say how it would all work in a film, but in a vacuum, the Spawn of Hastur are pretty unremarkable as far as monsters go, so I don't think they'd be useful on their own.