Thief

Thieving was a special ability that unique monsters could have in Diablo II prior to the release of Diablo II: Lord of Destruction that allowed them to knock items out of a character's inventory when hitting them with an attack.

This could initially be anything, including equipped weapons or armor, which could be especially crippling for physical attackers moreso than mages. This was nerfed to only make players drop Potions out of their Belt.

With the initial sale of Diablo II prior to patching, Lord De Seis had this unique ability to 'steal' character's items. On a successful hit, he had a % chance of making a random item the character had equipped drop onto the floor. This was changed to potions later to reduce its effectiveness.

The current version of Diablo II does not have any unique with this ability. It was removed because it was very game-crash inducing. It could also be an issue in multi-player if other players picked up dropped items.