In a recent game, for example, my players fought the nightmarish remnants of a man who was driven insane by Lovecraftian cultists. His nightmares appeared as a cloud like a galaxy that distorted space and time around the players until they couldn't tell what was directly in front of them and what was as distant as the stars that appeared in the cloud. Mammoth faces appeared and disappeared in the cloud, at one moment distant as the stars and the next moment next to the character, screaming and biting mercilessly at the PCs' exposed flesh. Every now and then a comet or shooting star would flash in front of the party, blinding them with brilliant light.
Hmm... a creature with
-A constant confusion effect
-Multiple bite attacks
-A blinding attack every other round
Yep: it was a gibbering mouther. Only described in different terms that (I believe) appropriately freaked out my players. After the session I told them what it was, and one of them commented, "I had no idea how nasty gibbering mouthers were!"
Truth is, it wasn't any nastier than normal. It just looked it, and because the PCs weren't able to put a label on it, the battle was scarier.
Dressing up monsters in different clothes is a lot of fun, and can go a good way toward giving your adventures the appropriate ambience. I much recommend it.