SRD:Robe of Vermin
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Robe of Vermin: The wearer notices nothing unusual when the robe is donned, other than that it offers great magical defense (as a cloak of resistance +4). However, as soon as he is in a situation requiring concentration and action against hostile opponents, the true nature of the garment is revealed: The wearer immediately suffers a multitude of bites from the insects that magically infest the garment. He must cease all other activities in order to scratch, shift the robe, and generally show signs of the extreme discomfort caused by the bites and movement of these pests.
The wearer takes a –5 penalty on initiative checks and a –2 penalty on all attack rolls, saves, and skill checks. If he tries to cast a spell, he must make a Concentration check (DC 20 + spell level) or lose the spell.