The Abath was thought to be creature similar to a European Unicorn that was first found in documents dating around the 16th century. Supposedly, Edmund Barker, a member of James Lancaster's crew traveling to East India had thought they bought several female unicorns' horn.
"This abath is certainly Sumatran or Javan rhinoceros, in Malay called بادق‎ bādaḳ. The qaf is usually silent, so the word "bada" was coined by Portuguese travelers. Ending in "a", it seemed feminine to their ears and was assigned the feminine article, "la bada", and sometimes misinterpreted as "l'abada" "Abath" is a variant of this word."
According to Grimm fairy tails, this creature would impale its horn into human children and would eat them afterwards. The stories also claimed that this creature prefered the dark, though it could be seen and heard.

Realistically this was probably just a rhinoceros. Though some claim they are different from the descriptions from the folklore. This creature is classified as mythological and for some, debunked.

Citing:
http://cryptidz.wikia.com/wiki/Abath
http://grimm.wikia.com/wiki/Abath
http://www.fanforum.com/f421/die-wesen-grimm-%7C-wesen-week-1-something-wesen-comes-way-63105079/index16.html#post75099597