Sword of Sharpness
Weapon (any sword that deals slashing damage), very rare, requires attunement · 2014 rules, SRD 5.1
Max damage vs objects; on a natural 20 an extra 4d6 slashing and roll a d20: on a 20 you lop off a limb. Can shed light.
Also in the 2024 rules (SRD 5.2).