My bard is wearing the Puck's Cap and it doesn't seem to be hurting her performance. Piety does determine stamina to some degree, which the bard requires a lot of to use the instruments, so it's was a tradeoff early levels on when her stamina was low though.
If a cursed weapon is used, then the char cannot swap to a long range weapon, so there is a bit of a limitation there..
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So how does one become a member of the Illuminati anyway, eh? Is it a forefather thing?