A melee weapon of pure force springs into existence and attacks a designated opponent when he provokes attacks of opportunity, but no more than once per round, dealing 1d8 points of damage per hit with a critical threat range of 19–20/×2. It also grants any creature attacking this opponent a flanking bonus, though the weapon does not gain this benefit. The weapon is visible and takes the shape of any appropriately-sized simple or martial weapon you desire. It uses your caster level plus your relevant caster ability modifier as its attack bonus. It strikes as a spell, not as a weapon, so, for example, it can strike incorporeal creatures. The weapon follows the foe you choose as long as he remains within range. Occupying the same area as the foe, it makes attacks of opportunity whenever that particular foe provokes him, but otherwise it takes no actions. Your feats (such as Weapon Focus) or combat actions (such as charge) do not affect the weapon. If the weapon goes beyond the spell’s range, the spell ends. Once you’ve designated a foe, you cannot choose a new opponent to target with this spell.
The irksome weapon cannot be attacked or damaged. If an attacked creature has spell resistance, check for resistance the first time the irksome weapon strikes it. Successfully resisting the weapon dispels the spell.