Babaušis
Babaušis (š-sh) is a chthonic creature, evil spirit that dwells in dark places. People used to scare children with him. There were sayings such as: Don’t go outside after dark, Babaušis will get you; I wouldn’t be alone, I am scared of Babaušis; Babaušiai are sneaking in to the dark corners. What’s interesting that Babaušis can also mean a snot, although this name for it is almost never used nowadays.
There are no suggestions of how he should look like because that way is even scarier - you don’t know what to be scared of, so you are afraid of the worst things you can imagine and then of the dark itself.