The Power of Unknown Monsters

Ssu picture from Tekumel.com

I've been using Arduin and Empire of the Petal Throne monsters in my gam: Mnor, N'grutha, Phraint, Hlus, Shunned Ones and Ssu, and I've noticed that the players are terrified of these "alien" monsters, they have no idea what they are dealing with and it puts the fear into them! I imagine the earliest D&D players having a similar reactions to Umber Hulks, Beholders, Mind Flayers, etc.

Being "unknown," without any concrete references to what you are dealing with makes these things far more intimidating, and also has a nice "genre simulationism" effect, as many situations in the source literature deals with similar circumstances. As well, by keeping monsters alien and unknown you are keeping them fresh, avoiding the "re-run" effect.

In my game there may be a brief exposition and a name provided when the creature is initially encountered or heard about, but it generally isn't enough for the player to get a firm handle on what to expect. This of course can scale according to how much of the monster's nature you want to be an unknown factor. Common animals versus a cosmic horror emerging into the universe for the first time providing examples form each extreme of the scale.

The Tekumel creatures in the underworld beneath Pi, the Hluss, Shunned Ones and Ssu, were characterized as terrifying, mysterious subterranean bogeymen. The miners that hired the characters were characterized as not having a firm idea of what they would be dealing with, only providing guesses. Guesses that did prove to be accurate, however.