Vorpal sword

A vorpal sword is a greatsword, longsword or scimitar that can behead opponents on lucky strikes.

Description
The wielder gains a +3 bonus to attack and damage rolls. Additionally, attacks made with this weapon ignore resistance to slashing damage.

When the wielder rolls a 20 on an attack roll, they can cut off one of the target's heads, killing the target instantly unless it can survive without the head. A creature that is immune to slashing damage, has legendary resistances, lacks a head or doesn't need its head is immune to the decapitation effect. Additionally, a GM may decide a creature's head is too big for this action to be feasible. In these cases, the target instead takes an extra 6d8 slashing damage.

History
Derrig had a vorpal longsword. However, he did not roll a natural 20 on his attack roll to decapitate an opponent.

Trivia
The name "vorpal sword" comes from Lewis Carroll's poem "Jabberwocky".