Ok, now this this seems like a sub-heading for SHOW not TELL? Is that true?
Specificity is a wonderful thing. It brings things to life. Rather a boring old abstracted thing "it is scary", you can instead build a certain vibe by being specific and instead describing things that are scary. This helps turn the routine of "Yet Another Creature Encounter" in to something more memorable. Showing, instead of telling. One way to do this, with creatures, is to give them a name.
I'm not referring to Vargash the hobgoblin, Frank the bandit or Fen'Gol the orc. There are two common ways to do this well. The first is to change the indefinite article article to the definite article, which is just a fancy way of saying "the THE instead of A/AN." It's not that A troll lives under the bridge, instead THE troll lives under the bridge. Or, think of THE dragon or THE medusa. There could be one of two things going on. Either this is the ONLY one of those creatures, hence the THE, or it's the only one that matters to the people at hand. They don't usually encounter dragon in the village of Bogtown, dragons being only a legend. So when one moves in it is THE dragon instead of A dragon. This adds to the mythic nature of the beast. It's not just another old boring "a blah blah blah." It's not routine. It's a threat. It's THE ogre.
Another way to handle this is to give them a name that is both more and less specific at the same time. It's not a plain old gang of bandits. Instead they are Shorty Bills gang or Fat Mamma Cass's boys. Specificity. Now they are instantly more memorable than just a plan old "there is a group of bandits here." Likewise "the troll of Boggstown" or "the Hangertown ghost" are both better than just saying "a troll."