Thought you could escape?
Stalker enemies are similar to 'The Persistence of Bossery', but with a few key differences. The first is that they aren't typically fought in isolated fights, instead it's best to look at it like one extended fight. A perfect example can be found in Resident Evil 2.
Mr X is an enemy fought throughout Resident Evil 2's story, making his entrance after the player works hard to clear a path through a blocked corridor and then he just sort of pushes the obstacle (crashed helicopter) aside with one arm. From then on, the game is afoot. Mr X will stalk (that's where the name comes from!!!) the player for the rest of the time that they're in the Raccoon City Police Department, following them unless they're able to escape or outrun him. Although he does move slightly slower than the player he is very persistent, he cannot be killed and it takes an extraordinary number of bullets to bring him to his knees for a few seconds. This makes direct combat useless, all it will do is waste the player's time and resources. He essentially becomes an environmental hazard that the player has to keep constant track of, mentally blocking off routes based on when they last saw him. By itself this isn't too much of a challenge, just keep moving. What makes Mr X slot into place as a formiddable boss is the wider gameplay of RE2. The game's focus on backtracking and inventory management to complete puzzles that gradually unlock a wider map means that players will come into contact with Mr X far more than they would with completely linear level design. Also complicating things are that all the game's regular enemies are still present, meaning the player has to juggle dealing with their inventory, common enemies and Mr X all at the same time. Shooting a zombie in one room might reveal their position to Mr X, who could block off the only escape route in a room with a critical puzzle in.
While Mr X does have the occasional scripted appearance and cutscene, the majority of player encounters will be unique and dependent on the status of the game and their actions. i spoke about this ages ago in a post called 'Threatening Antagonists', but this makes encounters with Mr X feel much more personal and intimately terrifying. Quickly comparing Mr X to Chris Walker from Outlast, a boss that straddles the line between 'The Persistence of Bossitude' and a stalker enemy. Chris Walker only appears at specific points, but Outlast's gameplay of 'no combat just hide and cry' makes these encounters feel like a mini stalker arena. Chris' (we're on first name terms) encounters typically involve him making a sudden appearance, with the player having a brief period of time to hide before he's on the prowl. He will then patrol the surrounding area in search of the player, while they're tasked with completing some objective in order to proceed, finding an escape route or running away (probably while crying).
Stalker enemies are really cool. They're a perfect fit for horror and survival horror, giving players a constant sense of tension not knowing where they are or if they've got the resources to deal with them. Outside of horror titles i can't think of any examples (except maybe the Glyphid Stalker in Deep Rock Galactic - but that's a good example of a stalker miniboss rather than a true boss), they're such a perfect fit for creating that oppressive atmosphere typical of horror games. Also can we briefly mention how funny it is that Mr X is classified as a bioweapon but he's just a large man that punches people.
Thank you for reading, that's definitely the end now, 100%, no other types of boss, no siree, that's all of them. Forever.