Hrunting

Hrunting was the magical sword given to Beowulf by Unferth in the ancient Old English epic of the same name. Beowulf used it in battle against Grendel's Mother.

The sword possessed great power and never failed anyone who used it, however when Beowulf descended to the bottom of the lake where Grendel's Mother dwelt, the sword lost its power and the Hrunting was ineffective against the creature. Beowulf instead searched the inside the lair and found a sword which belonged to the Jotuns, which only he was strong enough to lift. Beowulf used this sword to kill and decapitate Grendel's Mother, but her poisonous blood melted the Giants' sword's blade like wax.

Beowulf returned to the surface with the head of the monster (and the hilt of the sword) as proof of his victory.

"And give Unferth my old heirloom,:my splendid wavy sword:widely known among men:to have a hard edge.:I will do my glory work:with Hrunting—or:death will take me"

A sword called Hrunting appears in the video game Castlevania: Aria of Sorrow as a sword with the ability to poison enemies, and in Final Fantasy X as a sword customized with the SOS Overdrive ability.