Eating stalker meat will stun the player and turn them temporarily invisible for 50-149 turns if they are not already invisible; if eaten while already invisible, the player will become permanently invisible and gain the see invisible intrinsic. Wearing a mummy wrapping counts as being visible for this purpose.
Stalkers are always generated invisible as indicated above, and will always be hostile.
The stalker is the second quest monster for Samurai, and makes up 14% of the monsters randomly generated in the Samurai quest. Stalkers are also generated upon the initial creation of each quest level: one each on the home and upper filler levels, nine in the locate level, three in the lower filler level(s), and nine at the goal level. Stalkers are also part of the first quest monster class for Monks and the second quest class for Samurai.
Stalkers can hit fairly hard with their single attack and move at the same speed as an unburdened, unhasted player - in addition to being invisible, their "stunned" effect causes them to move erratically, making them annoying to face or avoid unless you have a means of detecting them (e.g., see invisible or telepathy).
Stalker meat is one of the more reliable sources of the see invisible intrinsic, either through eating two separate servings in quick succession or else eating one with a worn source of invisibility. As eating stalkers stuns you, be sure to avoid doing so in the midst of battle unless you can cure it quickly (e.g., with a unicorn horn); keeping a mummy wrapping around is also advisable if you plan on shopping at any point afterward.
The stalker has been present in the game since PDP-11 Hack, a variant of Jay Fenlason's Hack. From this version and the first releases of Hack 1.0 until NetHack 3.3.0, the symbol I was used to represent the stalker (I meaning "invisible"). Starting with 3.3.1, the stalker was moved to the E class, and I instead indicates the last known position of any invisible monster.
The invisible stalker is a monster that appears in Dungeons & Dragons, which is a type of air elemental; this is likely the basis for making the stalker part of the elemental monster class, and may explain their ability of flight. As most versions of Hack and NetHack automatically prefix monster names with "invisible" when relaying actions referring to an invisible monster, the word "invisible" is dropped from the monster's name to avoid the redundant "invisible invisible stalker".
- You permanently gained the invisibility and see invisible intrinsics by eating a stalker corpse while already (temporarily) invisible.