Vorpal jabberwock (UnNetHack)
(content pulled as is from the GruntHack page--a quick source dive didn't reveal any obvious differences but there might be some. More importantly, if you came to this page you probably just want to know one thing--yes, it WILL behead you!)
The vorpal jabberwock is a monster in UnNetHack, derived from the deferred feature in NetHack. It is a more powerful jabberwock (Vorpal Blade will still behead them), possessing two beheading attacks - 1 in 40 successful hits it lands beheads you, killing you instantly (this is a 100% chance if you are polymorphed into a jabberwock or vorpal jabberwock yourself). Polymorphing into a headless or amorphous form will protect you, as will cancelling the vorpal jabberwock.
"Beware the Jabberwock, my son!
The jaws that bite, the claws that catch!
Beware the Jubjub bird, and shun
The frumious Bandersnatch!"
He took his vorpal sword in hand;
Long time the manxome foe he sought --
So rested he by the Tumtum tree,
And stood awhile in thought.
And, as in uffish thought he stood,
The Jabberwock, with eyes of flame,
Came whiffling through the tulgey wood,
And burbled as it came!
One, two! One, two! And through and through
The vorpal blade went snicker-snack!
He left it dead, and with its head
He went galumphing back.