Quote from Fallenstar004>>

’Twas brillig, and the slithy toves

      Did gyre and gimble in the wabe:

All mimsy were the borogoves,

      And the mome raths outgrabe.

“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.

“And hast thou slain the Jabberwock?

      Come to my arms, my beamish boy!

O frabjous day! Callooh! Callay!”

      He chortled in his joy.

’Twas brillig, and the slithy toves

      Did gyre and gimble in the wabe:

All mimsy were the borogoves,

      And the mome raths outgrabe.

- Louis Carol, the Jabberwocky

so this is like a god sword?

peanus

Nice.

I have this sword now maybe my dm will let me decapitate the teraseque I’m unstoppable ha ha ha

It's 6d8 on top of the normal damage on the table below the description. Normally on a 20 you'd roll your typical damage twice (some people just double). With this sword you'll roll 6d8 instead of a second normal damage roll. 6d8 is much greater than all the damage specs in the table and very high for a melee weapon in general anyway, so it's a win/win.

Common sense, instant death through decapitation is already very overpowered. I feel like 12d8 extra damage on a nat 20 isn't broken considering that this sword can insta kill anything without legendary actions, essentially. (Size doesn't really matter considering at the level you would be given this you would have plenty of ways to increase your size, e.g path of the giant barbarian or rune knight fighter + enlarge reduce spell. You can literally become gargantuan by 14th level as a giant barbarian with a spell caster in your party casting enlarge reduce on you. I'd argue that a gargantuan fighter/barbarian with a gargantuan sword could easily chop of the head of a gargantuan dragon.)

Quote from sheridancaulin >>

It's 6d8 on top of the normal damage on the table below the description. Normally on a 20 you'd roll your typical damage twice (some people just double). With this sword you'll roll 6d8 instead of a second normal damage roll. 6d8 is much greater than all the damage specs in the table and very high for a melee weapon in general anyway, so it's a win/win.

Came here to say that this is the correct interpretation. You don't "Crit" the 6d8 and double that. In this instance, the bonus 6d8 damage is what you get for rolling a natural 20 against certain targets.

wowee, this item is so coolio!

Quote from Anyonewhosmellslikepoo >>

I have this sword now maybe my dm will let me decapitate the teraseque I’m unstoppable ha ha ha

 lol

I have a tattoo of the art of this! Loved this weapon since I was a kid.

Quote from Medirby >>

Since the 6d8 only applies on a 20 roll on creatures with no heads, and since a 20 on an attack roll is a critical, do the 6d8s naturally become 12d8 or does it stay as a 6d8?

 Do regular critical damage, and then add 6d8. Example- Vorpal Greatsword crit: 4d6+6d8