Stalker

The Stalker is the mature version of the Larval Stalker and both share many characteristics with the Grey Child and the Mumbler, with the main differences being that their bodies are partially corporeal; they are translucent with a dark aura around their bodies.

However, unlike their younger versions the Stalker seems to have a more physical presence and therefore can now actively harm Harry Mason when he encounters them (Larval Stalkers simply observe and stand around Harry). They are equipped with a special invisible knife and if they spot Harry, they will wander over to him with the view that Harry may assume that they are a harmless Larval Stalker and not bother to engage. However, they are aggressive and will continually attack Harry, sometimes in groups.

On the flip side, their bodies now have more physicality to them and Harry can hurt them back whether it be with melee weapons or guns. When they die, they will disappear and not return.

In terms of their symbolism, they are simply a dangerous version of the Larval Stalker and their meanings are the same - they represent Alessa Gillespie's isolation and loneliness at home and at her school.

Interestingly, the Stalker appears to be the same character model and has the same behaviour as the Grey Child and are present in the censored versions of the games where Grey Children were removed due to them looking too much like a real human child… so, quite a puzzling contradiction. Also, in the game they appear as essentially black due to the PlayStation hardware not being able to render translucent objects realistically.