I would like to inquire about the Hashashin during the Fatimid era.

The Hashashin (Assassins) are an Ismaili (Nizari) sect that originated in Egypt at the hands of Hassan-i Sabbah, and spread throughout the Levant and Persia. They were named so due to their extensive use of hashish. Their beliefs are identical to those of the Ismailis, such as belief in an infallible Imam from the lineage of Muhammad ibn Ismail, the concept of the Hidden Imam, elevating their imams to a status close to divinity, in addition to the belief in transmigration of souls (reincarnation). They carried out revolutions and assassination attempts against Muslim rulers, and had a state called "the Eastern Nizari State" until it was eradicated by Hulagu the Mongol.