It does not prevent the casting of spells by clerics, bards, shamans and paladins. Some deities take considerable exception to people who place these items on their temporal proxies. The consequences of such displeasure is up to the DM in charge.
The helm has several useful side effects. First, the helmet will allow the user to see/sense every living creature within a 100 foot radius, though walls and barriers, even if the targets are hidden or invisible. Living creatures appear as glowing, ghost like shapes which become more indistinct over distance and intervening materials. Someone in the helm will sense barriers and walls a fogginess in front of living beings.
The wearer cannot be surprised by living creatures. This useful feature is mitigated by the fact that the user only has a hazy awareness of non-living objects, barriers or walls. They can sense enough to walk, hands out before them, but they have a -4 to strike or perform any task that requires the senses blocked by the helmet. Without a living creature to orientate on, the wearer cannot sense walls and barriers. The helm does not impact the users ability to defend themselves from living things at melee ranges, the wear still receives an AC bonus for Dexterity. This does not apply when the attack comes from a non-living creature or a missile weapon.
If a potion is brought to the mouth area of the helmet, the wearer will know if the potion is magical, poisonous, or mundane and know if it is safe or unsafe to drink. The wearer will not know the purpose of the item. Alcohols register in a unique fashion due to the nature of the beverage.
The helm renders the wearer invisible to all undead but does not reveal the presence of undead. Intelligent undead can guess the wearer's presence, but have a hard time tracking the wearer if they stay motionless or move quietly.
The history of the helm is lost. The obviously usage is to force a magic user to wear the helm while restrained. The loss of sight and sound while remaining aware of living threats was probably a happy benefit when forcing confessions from witches and the like. Player characters will probably find other uses for it.
|Emulous Cursed Sword
|The Symbol of Sol Invictus
|Shape of Memory
|Staff of Eyes
|Shield of Force
Now, the commercial. I have a little book called Zero to Hero: Uncommon Commoners, over at DrivethruRPG. Also on Drivethru is my custom character sheet for AD&D and Unearthed Arcana.
I am obviously thinking of writing another and Gnolls might be the subject. Please let me know what you think in the comments.