They can be dangerous, as they counter magic attacks with Roulette, and can use Doom and Dread Gaze, all attacks that work to kill party members in some fashion. They often appear in groups of three, or together with a Cherry or Daedalus. They have no elemental weaknesses.
The Ahriman never uses its special attack called Critical, rendering it a dummied feature.
With MP-intesive spells like Death and Banish, there's a chance Ahriman will run out during battle, which is especially good if the player has low Stamina and Magic Evasion. Being equipped with Safety Bit/Memento Ring will grant immunity to 75% of its attacks.