Shan (Insects from Shaggai)

The Insects from Shaggai, also known as Shan, came to Earth many years ago and became stranded due to a component in our atmosphere. They are a highly advanced race which enjoy torturing other races for whatever reason. They can also phase through solid objects, which they use to enter a human's brain to tinker with it.

In the RPG...

The size of a pigeon, and with only 1 hit-point, they are easily disposed of, but if they are present, there's a good chance that they've co-opted the minds of any number of locals and have them under their sway. This is because Shan can become intangible and enter the brain of a human, wherein they can progressively take control. This requires an opposed POW roll, though with their 80 POW they have a 77% chance of achieving this against an average human. No one really knows how to remove one, either.

    Shan don't have any means to attack on their own, so either use those they're inhabiting to fight, or a special weapon called a "Nerve Whip". This whip relies on an opposed POW roll instead of a Fighting roll, however, so as mentioned above, its effectiveness is essentially 77%. It doesn't cause any damage though, merely incapacitating its target.

    There are two stat changes of note in the 7e Malleus Monstrorum, the first of which is that their DEX has been reduced from 155 to 85. I feel that being like an insect should have granted them a high dexterity, so this is one change I don't agree with. INT and POW have changed too, though there averages are roughly the same, so it's not really an issue. The other big change is that the Shan's Flying Move rate has been halved—from 40 to 20. According to the 7e Rulebook, 20 Move is the equivalent to 1000 mph—that's Mach 1.3! 
    If the Investigators should discover a colony of Shan, they will discover that they have also enslaved beings from Xiclotl and L'gy'hx as guards. Neither race would be easily dispatched, so avoidance is probably the best strategy.

In a video game...

As in the RPG, I don't imagine the Shan would pose much of a direct threat to a video game protagonist. They are very small though, making them a pretty difficult target.

In a film...

Conceptually, the Shan fit into the now-cliched trope of government subversion and conspiracy, or on a larger scale, something akin to Invasion of the Body Snatchers. Even if that could be written in a new and fresh way, I think the creatures themselves would look pretty hokey on-screen. No matter how cool they look aesthetically, seeing a large insect tittering about with technology would be pretty laughable. Even just the thought of it is now reminding me of The Outer Limits episode, "The Zanti Misfits":