(Yeah, so you've gotten two versions of Excalibur. One hates you and the other was made by the deep ones. Deal with it.)
The legendary sword of King Arthur, also known as Caladbolg, Calesvol, Caliburn, and Excalibur. Somewhat exaggerated, the blade known as Caledfwlch is actually a hand-hammered dagger. Despite its rough-hewn quality, it is sharper than most blades known, having been made with a combination of standard crafting techniques and Mythos magic. Crafted by deep ones for some unknown purpose, this dagger has strange pictographs carved on both sides of the blade (it reads "Born from the sea" on one side and "Return to the sea" on the other in R'lyeh glyphs). The coral hilt and crossguard bear various pictographs featuring a fish motif; a successful Cthulhu Mythos roll recognizes the hallmark of the deep ones.
Despite its small size, Caledfwlch has several qualities of a larger sword (perhaps owing to its usual depiction as a sword). Like a sword, it can Parry and Knockout. It is otherwise treated as a Large Knife, and its base chance increases with Large Knife.
Most importantly, the dagger is enchanted. It can damage Mythos beings as if the subject of a Bless Blade spell. It also ignores all armor, and has a fearsome base damage.
Relevant statistics are listed below:
base chance — 15%
damage — 1D8+2+db
hands — 1H
attacks — 2
HP — 25
The dagger even has a magic scabbard that helps reduce wounds. As long as the character has the scabbard on his person, all wounds deal the minimum possible damage, and the character cannot be knocked unconscious from shock or loss of hit points. The character falls unconscious and dies normally from being reduced to two or fewer hit points, and enchanted weapons deal their normal damage.