The ring of protection from shape changers, cost 100, has a number of effects (in addition to the normal ring hunger):

• Chameleons, mimics, doppelgangers, and sandestins appear in their normal form.
• Werecreatures appear in human form and thus cannot infect you with lycanthropy. They are also prevented from summoning help.

Dropping a ring of protection from shape changers into a sink produces the message "The sink looks nothing like a fountain."

A non-cursed 100 zorkmid ring can be identified as protection from shape changers by wearing it in a shop, on the top level of Sokoban, the rogue quest, or anywhere where mimics are known to be. A ring of protection from shape changers will uncloak the mimics.