Ring of Pain

Intimidate is a mechanic that works as a stun. It stops the enemies from retaliating when triggered, allowing for a free follow up hit. Keep in mind that the enemy must survive the first attack for the effect to register. A one hit kill will not count.

There are only a handful of items that can inflict intimidate on attack.

They are

Mask - False Confidence (Blue Item)
Gauntlet - Power Glove (Purple Item)
Necklace - Trophy Amulet (Purple Item)
Charm - Berserker Relic (Purple Item)

(Color Corresponds to chest color needed to find the item outside of shops or Finders Keepers)
Simply equip one of these items and attack 250 different creatures over the course of your games.