Omen Staff is a post-Superancient tier summon that is the EX variant of Raven Staff. It summons a crow minion to fight for you, which relentlessly attacks enemies.
Its best modifier is either Ruthless for the highest damage output or Mythical for a wide array of stat bonuses except critical strike chance as minions cannot deal critical hits. If you want more damage and knockback as well as reduced mana cost, go for either Mystic or Masterful.