The Ogre Club is an artifact added in the Heroes V: Tribes of the East stand-alone expansion pack. It goes in the Weapon slot and it increases the hero's Attack by +5, but decreases the Initiative of all the creatures in their army by -5%. The Club can be purchased for 8,500 gold. It is part of the Weapons of Might set.
Adding so much to Attack is great, but a drop in Initiative, though small, may have negative effects, particularly when facing ranged or spellcasting neutrals. By acting first, these foes inflict casualties in the beginning, and these losses are hard to reverse even with Resurrection or Raise Dead. Perhaps Barbarians are more suited for this item because it raises the chance to kill enemy stack and increase rage points. All in all, one has to be cautious when equipping this item.