History UniqueEnemy / HalfLife

* Two Bradley [=IFVs=] appear in the ''Half-Life'' chapter "Surface Tension", one of which has a TOW missile launcher while the other doesn't. They don't show up again.

* In the original ''VideoGame/HalfLife1'', the Black Ops assassins only appear in two rooms in the entire game, and even then only in groups of three. In ''[[VideoGame/HalfLifeOpposingForce Opposing Force]]'', they're more common and have more variations, but only slightly so. This is due to the fact that by the time Shepard wakes up from his crash on day 1, the government was only waiting for the final evacuations to complete before silencing the surviving civilian personal and stranded soldiers on day 2, while the small teams Gordon faced on day 1 were probably there as advanced recon.

* While common in the last levels of the original game, the Alien Controllers only appear once in ''Opposing Force'' during the part where Shephard sees Gordon and once in ''Blue Shift'' when Barney is calibrating the teleportation transponder in Xen.

* In ''Half-Life'', only three ceiling turrets appear in the game. Two of them are encountered in "Office Complex", and the third one, much larger than the first two, is encountered near the start of "Forget About Freeman".
* The tanks encountered in ''Surface Tension'' on the first game count as there's only a few and no two are alike, some have turrets with a [[FixedForwardFacingWeapon very limited rotation range]] making you safe as long as you are behind them, while others can turn a full 360. Some shoot rockets while others have some sort of {{hitscan}} mortar type weapon. Finally, while most have only one gun there's one with a machine gun type weapon in addition to the main (rocket) turret. ''Blue Shift'' only has one tank to fight.
* In ''Half-Life'', the first area of Xen has ceiling turrets resembling gaslamps placed around the perimiter of the central island, zapping any intruders who attempt to break into the teleporter inside. They're not used anywhere else.

* In ''VideoGame/HalfLife2'', the Claw Scanners appear in a couple of chapters and don't appear again until late in ''Episode One''.

* In ''Half-Life 2'' and ''Episode One'', Manhacks were a common enemy, but in ''Episode Two'', they are only encountered once, when the Combine breach White Forest.

* In the ''Half Life Alyx'' chapter "Captivity", you can find a single headcrab zombie wearing a tiger mask. No others are encountered elsewhere in the game.

!!''VideoGame/HalfLife''

!!''VideoGame/HalfLife2''

!!''VideoGame/HalfLifeAlyx''

!!Fan Games / Mods

* The Antlion Guardian in ''Episode Two''. Essentially a PaletteSwap of the normal Antlion Guard with a poisonous status effect added to its attacks, it's only encountered once in the entire game.

* In ''VideoGame/HalfLife2'', the Claw Scanners appear in a couple of chapters and don't appear again until late in Episode 1.

* The Civil Protection officers were a common enemy during the early chapters of ''Half-Life 2''. In ''Episode One'' however, just a single squad of them appear during the last wave of the EscortMission at the end of the game; they're then completely absent from ''Episode Two''. ''Episode One'' also uses the Gunship and Strider for one-off boss battles, both of which were more numerous in ''Half-Life 2'' proper. In addition, only one Antlion Guard is fought in ''Episode One''. Plus one Combine APC.
* The Antlion Guardian in ''Episode Two''. Essentially a PaletteSwap of the normal Antlion Guard (but otherwise identical), it's only encountered once in the entire game.

* The [[OvershadowedByControversy much-maligned]] fangame ''VideoGame/HuntDownTheFreeman'' has a supposed {{Antepiece}} involving a medkit thief getting eaten by a barnacle near the start of the game. The rest of the game has no other barnacles.
* In ''VideoGame/BlackMesa'', there is a single HECU headcrab zombie in "Power Up" attached to an IV stand which actually moves with it as long as the zombie lives.

[[UniqueEnemy Unique Enemies]] in ''VideoGame/HalfLife'':
* In ''VideoGame/HalfLife2'', the Claw Scanners appear in a couple of chapters and don't appear again until late in Episode 1.
* Toward the end of the game, there is also one Overwatch Elite who uses a submachine gun, the only one in the game to do so (all others carry Pulse Rifles).

* The Civil Protection officers were a common enemy during the early chapters of ''Half-Life 2''. In ''Episode One'' however, just a single squad of them appear during the last wave of the EscortMission at the end of the game; they're then completely absent from ''Episode Two''. ''Episode One'' also uses the Gunship and Strider for one-off boss battles, both of which were more numerous in ''Half-Life 2'' proper. In addition, only one Antlion Guard is fought in ''Episode One''. Plus one Combine APC.
* The Antlion Guardian in ''Episode Two''. Essentially a PaletteSwap of the normal Antlion Guard (but otherwise identical), it's only encountered once in the entire game.
* The Fast Zombie Torso, also in ''Episode Two'', appears a handful of times throughout the game. Fast zombies normally can't survive their legs being ripped off, unlike their standard cousins.
* The [[OvershadowedByControversy much-maligned]] fangame ''VideoGame/HuntDownTheFreeman'' has a supposed {{Antepiece}} involving a medkit thief getting eaten by a barnacle near the start of the game. The rest of the game has no other barnacles.

* In ''Half-Life 2'' and ''Episode One'', Manhacks were a common enemy, but in ''Episode Two'', they are only encountered once, when the Combine breach White Forest.

* While common in the last levels of the original game, the Alien Controllers only appear once in ''Opposing Force''
during the part where Shephard sees Gordon and once in ''Blue Shift'' when Barney is calibrating the teleportation transponder in Xen.

* In the original ''VideoGame/HalfLife1'', the Black Ops assassins only appear in two rooms in the entire game, and even then only in groups of three. In ''[[VideoGame/HalfLifeOpposingForce Opposing Force]]'', they're more common and have more variations, but only slightly so.

* While common in the last levels of the original game, the Alien Controllers only appear once in ''Opposing Force''.
* Also in ''Opposing Force'', there is exactly one [[BlackHelicopter Black Ops Apache]].

* The tanks encountered in ''Surface Tension'' on the first game count as there's only a few and no two are alike, some have turrets with a [[FixedForwardFacingWeapon very limited rotation range]] making you safe as long as you are behind them, while others can turn a full 360. Some shoot rockets while others have some sort of {{hitscan}} mortar type weapon. Finally, while most have only one gun there's one with a machine gun type weapon in addition to the main (rocket) turret.

* The tanks encountered in ''Surface Tension'' on the first game count as there's only a few and no two are alike, some have turrets with a [[FixedForwardFacingWeapon very limited rotation range]] making you safe as long as you are behind them, while others can turn a full 360. Some shoot rockets while others have some sort of HitScan mortar type weapon. Finally, while most have only one gun there's one with a machine gun type weapon in addition to the main (rocket) turret.

* The alien auto-cannon. One appears in one corridor in the original game, having been set up by Alien Grunts, and nowhere else.

* In ''Half-Life'', the first area of Xen has ceiling turrets resembling gaslamps placed around the perimiter of the central island, zapping any intruders who attempt to break into the teleporter inside. They're not used anywhere else.

* In ''Half-Life'', Xen has their own version of ceiling turrets that appear on the large island that the player has to jump to in the "Xen" level. This island is the only location where the ceiling turrets appear.

* In the original ''VideoGame/HalfLife1'', the Black Ops assassins only appear in two rooms in the entire game, and even then only in groups of three. In ''Opposing Force'', they're more common and have more variations, but only slightly so.

* The tanks encountered in ''Surface Tension'' on the first game count as there's only a few and no two are alike, some have turrets with a [[FixedForwardFacingWeapon very limited rotation range]] making you safe as long as you are behind them, while others can turn a full 360. Some shoot rockets while others have some sort of HitScan mortar type weapon. Finally, while most have only one gun there's one with a machine gun type weapon in addition to the main (rocket) turret.

* In ''Half-Life 2'' and ''Episode One'', Manhacks were a common enemy, but in ''Episode Two'', they are only encountered once, when the Combine breach White Forest.