Phantoms
Psychic Emanations (or 'Phantoms') are rare monsters in Brogue that appear as an 'x'. Psychic Emanations can first appear on depth 2 and usually start out dwelling in bodies of water. Psychic Emanations can not be seen unless the player is currently telepathic, if the Psychic Emanation is standing in gas (such as the gas emitted from Blood wort Spores) or steam. Phantoms deliver slow, heavy blows to the player (such as an Ogre) and often flit at random moments and move very quickly. Phantoms health bars never appear on the screen even after you've hit them.
Tracking Phantoms[]
Phantoms also have a chance leave behind a trail of ectoplasmic residue whenever they move. This liquid appears like blood but when the cursor is hovered over it, the liquid is confirmed as Phantom Residue. This can be used to track a Phantom or see if one is nearby.
Monsters
Sometimes monsters will hide in walls or marble statues. They will also be described as Psychic Emanations.