Slaying of the Witch king

[The Saucepan Man]

Also, Merry broke the magic spell binding his unseen sinews etc.

The point being that his blade, which came from the Wight's Barrow, had been forged in the Kingdom of Arnor for use in battle with the Witch King's armies.

No other blade, not though mightier hands had wielded it, would have dealt that foe a wound so bitter, cleaving the undead flesh, breaking the spell that knit his unseen sinews to his will.