As a battering item, the Killing Edge can be swung to attack opponents, or thrown. About every three seconds, its blade briefly glows pink, and if the user swings it during this time, the damage and knockback dealt by the attack will be doubled. During these hits, the critical hit sound effect from the Fire Emblem Game Boy Advance titles will play. The tip of the blade is also more damaging than the base.
The Killing Edge is a sword that recurrently appears in the Fire Emblem series. It is notable as one of several "killer" weapons, a class of weapon that substantially boosts the likelihood of its wielder landing a Critical Hit. In the Fire Emblem series, a critical hit causes a weapon to deal three times its base damage, a trait that is reflected in Smash Bros. in the form of increasing damage and knockback when the sword is glowing. The Killing Edge's design in Ultimate appears to take inspiration from its appearances in Fire Emblem: Blazing Sword and Fire Emblem Awakening, with the weapon's shape and design resembling its appearance in the former, and the color scheme of the sword hilt resembling its color in the latter. Additionally, weapons will glow pink during critical hit animations from Fire Emblem Awakening onward.
Equipping the Ravio, Aegislash, Navarre, Lon'qu or Shadow Man Support Spirits will give the player a Killing Edge at a start of a match.