In NetHack, a shapeshifter or shape changer is a monster that can change form either randomly or at will.
List of shape changers
The various types of shapeshifters include:
- : chameleon
- @ doppelganger
- & sandestin
All other shapeshifters except for mimics will shift between forms under certain circumstances, dependent on the monster in question:
- Chameleons, doppelgangers and sandestins have a 1⁄6 chance of changing shape every turn, even while asleep (e.g. in a zoo). Polymorphing one yourself with a wand, spell, or potion will change its form as normal, but they will continue shapeshifting at random after.
- Werecreatures will randomly alternate between their human and animal forms, even while asleep, and polymorphing a werecreature will cause it to alternate between forms. This includes you if you are given lycanthropy from a werecreature's bite, unless you have unchanging or polymorph control.
- Vampires are often encountered in the form of a vampire bat, and will typically shift to fog cloud form to cross locked doors and certain other obstacles - vampire lords can shift to wolf form when not in sight of the player. A vampire may revert to their base form when attacking the player; killing a shapeshifted vampire will cause them to revive in their base form. Vlad the Impaler is capable of shapeshifting as well, but will not do so while carrying the Candelabrum of Invocation. Polymorphing a vampire will cause it to alternate between its base form and its bat (and/or wolf) form; if you are in the form of a vampire without polymorph control, you will do the same if you are either polymorphed again or else use the #monster extended command.
Examining any of the above monsters with a stethoscope or probing while they are in another form will identify them as shapeshifters. Wearing a ring of protection from shape changers will force them into their normal form; polymorphing any of the above monsters while wearing the ring will permanently change their form and remove their ability to shapeshift.
Mimics are an exception to much of the above, as they will instead take the appearance of various objects and sometimes dungeon features to catch the player off-guard. Interacting with a disguised mimic - e.g., by applying a stethoscope to one, attacking one, bumping into one, or throwing an item at one - will cause it to uncloak. As mimics do not take the form of other monsters, polymorphing will affect them normally (including system shock); protection from shape changers will force mimics into their true form and prevent them from disguising themselves.
- Using genocide on vampires and/or vampire lords would caused currently shapeshifted ones to become unkillable, as they could not return to vampire form properly. This was fixed in commit 757e6f9.
- Shapeshifters and other monsters that polymorphed into vampires would remain stuck in that form - e.g., shapeshifters would not take on new forms, a polymorph-produced vampire would not shift to bat or fog forms, and so on. This was fixed in commit 885de11 and commit 45ba0ad.