Arcane Blade, +1

An arcane blade can serve as an arcane focus in addition to being a magical sword that carries a bonus on attack and damage. When attuned by a spellcaster and used to cast an attack spell, it confers the same bonus to attack rolls for spells as it does for melee weapon attacks. In addition, if an attuned wielder succeeds on a critical hit when making a melee weapon attack with the arcane blade, they can forgo the normal additional effect of a critical hit and, instead, deliver the effects of an attack cantrip they know in addition to the normal weapon damage.

Proficiency with a Longsword allows you to add your proficiency bonus to the attack roll for any attack you make with it.

Notes: Bonus: Magic, Bonus: Spell Attacks, Castle Amber Conversion Guide and Expansion Original Adventure by Tom Moldvay Conversion to 5e and Expansion Notes by Stuart Broz, Focus, Versatile, Sap