The World Impaler was the highest pinnacle of High Elf magical worksmanship. It was made from the oldest branches of the World Tree.
This sword had two particularities that defied conventional understanding. Firstly, it could pierce through anything that existed in Firuman. Be it ethereal or physical, it could pierce through anything. Even space was not immune to it. It would be able to kill anyone you wanted dead if supplied with enough Legendary-level power.
There had been historical accounts of High Elves wielding the World Impaler with all their power to strike down their enemies 50 miles away.
Secondly, the sword was incredibly fast.
Due to its unimaginable speed, it was usually used in ambushes. A competent enough wielder of the sword would be able to strike their victim's vital points, ending them on the spot before they even realized what had happened.