Telepathy is a passive ability that allows players and monsters to detect non-mindless creatures, regardless of whether or not they can be seen visually. Telepathy comes in two types: the less powerful intrinsic telepathy and the more powerful extrinsic telepathy. Intrinsic telepathy only works when you are blind, and detects all non-mindless creatures on the level. Extrinsic telepathy does the same thing as intrinsic telepathy, but in addition it also works while unblind, to a maximum range of 8 squares.
Intrinsic telepathy can be acquired by eating the corpse of telepathic monsters, eating an amulet of ESP, or polymorphing into a monster with telepathy. Note that eating a (master) mind flayer will not grant you intrinsic telepathy if it grants you a boost to your intelligence. Intrinsic telepathy can also be gained after #praying to your god under certain circumstances.
- The Longbow of Diana
- The Orb of Detection
- The Magic Mirror of Merlin
- The Platinum Yendorian Express Card
Note that it is possible to have both intrinsic and extrinsic telepathy at the same time. In this case, the more powerful extrinsic telepathy is used.
Extrinsic telepathy can be lost by taking off an amulet of ESP (including The Eye of the Aethiopica) or a helm of telepathy. It can also be lost by dropping or bagging any of the artifacts that convey extrinsic telepathy.
- Spheres (including gas spores but not floating eyes)
- Elementals (excluding stalkers)
Pitfalls of telepathy
Mind flayers and master mind flayers can detect the location of PCs with telepathy, and attack them with a long-distance attack ("A wave of psychic energy pours over you! It locks onto your telepathy!").
Mindless monsters, such as golems, can easily sneak up on and attack unsuspecting players while they are blind and using telepathy, though if you are using telepathy in such a manner, chances are that any mindless monsters are very weak or you are strong enough to avoid taking serious damage from one attack.
As the article says at the beginning. Extrinsic telepathy behaves the same way as intrinsic telepathy when blind.
Some players may come to think that extrinsic telepathy doesn't grant telepathy over the whole level when blind. Usually, extrinsic telepathy is acquired well after intrinsic telepathy, and this can confuse some people. In variants, with more monsters competing with floating eyes for spawning, acquiring extrinsic telepathy first is less improbable.