npc_barnacle is a point entity available in 
Half-Life 2, 
Half-Life 2: Episode One, 
Half-Life 2: Episode Two, 
Half-Life 2: Deathmatch, and 
Black Mesa. It is a stationary, ceiling-mounted 'fishing' monster that tries to eat anything its tongue touches.
Barnacles were originally devised in Half-Life as a simple way to limit movement in levels, and their function remains relatively the same in Half-Life 2.
Placement Tip:Most players prefer to avoid Barnacles altogether, so unless it's part of a puzzle, you might want to provide a way to get past without killing them.
NoteBy default, barnacles can only grab and eat NPCs specified in the game's code. Can be customized using relationships.
Warning:When a Barnacle grabs the player they may get stuck on ceilings, causing the barnacle to release them. 
Bug: In Black Mesa this causes the barnacle to become invisible.
Expand
(click to view enlarged images)
An example from d1_canals_02.
Black Mesa bug example in bm_c1a4b.
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Keyvalues
- Rest Distance (RestDist) <float>
- Distance above the ground that the tongue should lie when the barnacle is at rest.
BaseNPC keyvalues
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CBaseCombatCharacter:
- Relationship (Relationship) <string> !FGD
- <string|targetname or classname> <string|disposition> <int|rank>
- Changes whether this entity likes or dislikes certain other things. Used like the ai_relationship entity, with this entity as the subject.
- Values for
disposition are:
D_HT: HateD_FR: FearD_LI: LikeD_NU: Neutral
- Physics Impact Damage Scale (physdamagescale) <float>
- Multiplier for damage amount when this entity is hit by a physics object. With a value of 0 the entity will take no damage from physics.
CAI_BaseNPC:
- Target Path Corner (target) <targetname>
- The path_corner that this NPC will move to after spawning.
- Squad Name (squadname) <string>
- NPCs that are in the same squad (i.e., have matching squad names) will share information about enemies and will take turns attacking and covering each other.
- Hint Group (hintgroup) <string>
- Hint groups are used by NPCs to restrict their hint-node searching to a subset of the map's hint nodes. Only hint nodes with matching hint group names will be considered by this NPC.
- Hint Limit Nav (hintlimiting) <boolean>
- Limits NPC to using specified hint group for navigation requests. Does not limit local navigation.
- Sleep State (sleepstate) <choices>
- Holds the NPC in stasis until specified condition. See also Wake Radius and Wake Squad.
- 0: None
- 1: Waiting for threat
- 2: Waiting for PVS
- 3: Waiting for input, ignore PVS
- 4: Auto PVS
- 5: Auto PVS after PVS
- Wake Radius (wakeradius) <float>
- Auto-wake if player comes within this distance.
- Wake Squad (wakesquad) <boolean>
- Wake all of the NPCs squadmates if the NPC is woken.
- Enemy Filter (enemyfilter) <targetname>
- Filter entity to test targets against.
- Ignore unseen enemies (ignoreunseenenemies) <boolean>
- Prefers visible enemies, regardless of distance or relationship priority.
DamageFilter:
- Damage Filter (damagefilter) <targetname>
- Name of the filter_damage_type entity that controls which entities can damage us.
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Flags
ExpandBaseNPC flags
Wait Till Seen : [1]
- Prevents this NPC from seeing (or being seen) until it enters a player's viewcone.
Gag : [2]
- Won't make IDLE sounds until it's angry.
Fall to ground (unchecked means teleport to ground) : [4]
Drop Healthkit : [8]
- Causes this NPC to drop an item_healthvial upon dying.
Efficient : [16]
- Don't acquire enemies or avoid obstacles
Wait For Script : [128]
- Forces this NPC to "wait" in an idle state until it finishes playing a scripted_sequence.
Long Visibility/Shoot : [256]
- By default, increases a NPC's sight range to
6,000 units and allows it to attack from anywhere within that distance.
Fade Corpse : [512]
Think outside PVS : [1024]
- Allows this NPC to run its regular AI outside of any player's PVS.
Template NPC : [2048]
- Marks this NPC as a template for entities like npc_template_maker. The NPC will not spawn on its own. This is not needed for point_template.
Do Alternate collision for this NPC (player avoidance) : [4096]NoteThis flag is disabled in episodic for player companions, because the StartScripting input does this.
Don't drop weapons : [8192]
Ignore player push : [16384] (in all games since 
)
- Entity won't give way to player.
- Don't puke gibs immediately upon eating enemy. This does not stop them from randomly spitting out ribcage gibs after eating an enemy!
[todo tested in ?]
- Don't start with tongue down.
- Tongue will not penetate water : [262144] (only in )
- Barnacle's tongue will not penetrate water if this flag used.
- Don't spawn human skull on death : [524288] (only in )
- Barnacle will not spawn human skull on death if this flag used.
Bug:Doesn't work. [todo tested in ?]
Inputs
- DropTongue <void>
- Drop tongue towards the ground. Use in conjunction with Ambush Mode spawnflag.
- SetDropTongueSpeed <integer>
- Set Drop Tongue speed.
NoteIf the barnacle itself fires the "OnGrab" output to change this setting, it will also alter the "reel in" speed. Reel in speeds that are too fast will cause ragdolls to fly around.
- LetGo <void>
- Let go of anything I am holding.
- TongueTipUpdated <void> (only in )
ExpandBaseNPC inputs
CAI_BaseNPC:
- ActivateSpeedModifier !FGD
- DisableSpeedModifier !FGD
- Break
- Smash into pieces. If this is not possible, disappear.
- BecomeRagdoll (in all games since )
- Remove itself and instantly become a ragdoll with zero force (just go limp). OnDeath, etc. outputs will NOT be fired.
- ForceInteractionWithNPC <string> <string> (in all games since )
- Force the NPC to use a dynamic interaction with another NPC. Syntax is <targetname> <dynamic interaction>.
- ForgetEntity <targetname>
- Clears out the NPC's knowledge of a named entity.
- UpdateEnemyMemory (in all games since )
- Update (or create) this NPC's memory of of the given entity.
- GagEnable
- GagDisable
- Gagged NPCs won't speak (or moan, caw, etc.) unless made to be a choreographed scene.
- HolsterWeapon (in all games since )
- UnholsterWeapon (in all games since )
- Force the NPC to holster or unholster their weapon. Ignored if the NPC is scripting or if the NPC doesn't use weapons.
- HolsterAndDestroyWeapon (in all games since )
- Same as
HolsterWeapon, except the weapon is destroyed once it has been concealed.
- IgnoreDangerSounds <float>
- Ignore danger sounds for the specified number of seconds.
- InsideTransition !FGD
- OutsideTransition !FGD
- SetBodyGroup <integer>
- HACK: Sets this NPC's body group (from 0–n).
- SetEnemyFilter <string>
- SetHealth <integer>
- Set the NPC's health.
- SetMaxLookDistance <float> (only in
)
- Sets the maximum look distance for the NPC. Defaults are 2048 and 6000 for long range NPCs.
- SetRelationship <string|targetname or classname> <string|disposition> <int|rank>
- Changes whether this NPC likes or dislikes certain others. Used like the ai_relationship entity, with this NPC as the subject.
- Values for
disposition are:
D_HT: HateD_FR: FearD_LI: LikeD_NU: Neutral
- SetSquad <string>
- Change the name of this NPC's squad. Leaving the parameter blank will remove the NPC from any existing squad.
- StartScripting
- StopScripting
- Enter/exit scripting state, where NPCs ignore a variety of stimulus that would make them break out of their scripts. They ignore danger sounds, ignore +Use, don't idle speak or respond to other NPCs' idle speech, and so on.
- Wake
- Wakes up the NPC if it is sleeping.
CBaseCombatCharacter:
- KilledNPC !FGD
- Tells the entity it killed something. Despite the name, this can include a player. This input will be automatically sent by the victim when they die.
- physdamagescale <float>
- Scales damage energy when this character is hit by a physics object. With a value of 0 the NPC will take no damage from physics.
DamageFilter:
- SetDamageFilter <string>
- Sets the entity to use as damage filter. Pass in an empty string (no parameter) to clear the damage filter.
Outputs
- OnGrab <void>
- OnRelease <void>
- Fired when I attach/detach my tongue to/from something.
BaseNPC Outputs
Expand
- OnDamaged
- Fired when this NPC takes damage (!activator is the damage inflictor).
- OnDamagedByPlayer
- Fired when this NPC is hurt by a player (!activator is the attacker or vehicle driver [if friendly fire]).
- OnDamagedByPlayerSquad
- Fired when this NPC is hurt by a player OR by one of the player's squadmates (!activator is the attacker or vehicle driver [if friendly fire]).
- OnDeath
- Fired when this NPC is killed (!activator is the killer).
- OnDenyCommanderUse
- Fired when this NPC has refused to join the player's squad.
- OnForcedInteractionAborted
- Fired when the NPC aborts a forced interaction for some reason (target NPC died, couldn't be pathed to, etc.).
- OnForcedInteractionStarted
- Fired when the NPC starts a forced interaction.
- OnForcedInteractionFinished
- "NPCs in actbusies can no longer perform dynamic interactions."
Todo: What does this mean?
- OnHalfHealth
- Fired when this NPC reaches half of its maximum health.
- OnHearCombat
- Fired when this NPC hears combat sounds.
- OnHearPlayer
- Fired when this NPC hears the player.
- OnHearWorld
- Fired when this NPC hears a sound (other than combat or the player).
- OnFoundEnemy <targetname>
- Fired when this NPC establishes line of sight to its enemy.
- OnLostEnemy
- Fired when this NPC loses its enemy. Usually due to the enemy being killed/removed, or because this NPC has selected a newer, more dangerous enemy.
- OnLostEnemyLOS
- Fired when this NPC loses line of sight to its enemy.
- OnFoundPlayer <targetname>
- Fired when this NPC establishes line of sight to its enemy, and that enemy is a player.
- OnLostPlayer
- Fired when this NPC loses its enemy, and that enemy was a player. Usually due to the enemy being killed/removed, or because this NPC has selected a newer, more dangerous enemy.
- OnLostPlayerLOS
- Fired when this NPC loses line of sight to its enemy, and that enemy is a player.
- OnSleep
- Fired when this NPC enters a sleep state.
- OnWake
- Fired when this NPC comes out of a sleep state.
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Dedicated Console Variables
| Cvar/Command |
Parameters or default value |
Descriptor |
Effect |
| sk_barnacle_health |
35 |
int
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Barnacle spawn health. |
| npc_barnacle_swallow |
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bool
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Enable prototype swallow code. This makes the ragdolled yummy play the ACT_GESTURE_BARNACLE_STRANGLE activity. Cut in Black Mesa. |
| sk_barnacle_357_dmg_scale (only in ) |
1 |
float
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Magnum damage scale. |
| sk_barnacle_blunt_dmg_scale (only in ) |
1 |
float
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Blunt damage scale. |
| sk_barnacle_buckshot_dmg_scale (only in ) |
1 |
float
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Buckshot damage scale. |
| sk_barnacle_bullet_dmg_scale (only in ) |
1 |
float
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Bullet damage scale. |
Bugs/Limitations
Todo: Should we really keep the Portal related bugs? The barnacle is never even meant to be used in portal anyways, and the example gifs are not adding anything.
All
Tongue ignores objects with "$contents grate" and brush entities
If a Barnacle is placed above a prop using $contentsgrate, the tongue will clip through that object and the barnacle will release any object it grabs immediately.
The same will happen with brush entities, with the exception of func_physbox and func_physbox_multiplayer. func_detail and func_ladder are world brushes, so they are unaffected by this bug.
Eating its own gibs
Barnacles will sometimes try to eat their own gib models, and often try to eat the same few gibs nonstop. This has been fixed in 
Portal 2: Community Edition.
Todo: Is this actually a bug?.
Some NPCs becomes invisible
Some NPCs becomes invisible grabbed by a barnacle.
Todo: Which ones?
Some NPCs cause crash
If any of the following NPCs are grabbed by a barnacle, the game will crash: npc_combine_camera, npc_advisor, npc_rollermine, npc_portal_turret_floor, and npc_poisonzombie.
The only NPCs out of these that could realistically be grabbed are npc_rollermine and npc_poisonzombie, so if your map must have barnacles and one of these two NPCs in close proximity, make sure it also has clips around the barnacles to prevent them from interacting.
Todo: Find if there are more NPCs that may cause crashes.
Rocket turret's broken ragdoll
If a barnacle somehow manages to grab a npc_rocket_turret, the turret's ragdoll freaks out. Which is caused by the rocket turret not being meant to ever enter Ragdoll mode.
Gibs don't traverse portals
Gibs spawned by barnacles do not pass portals, as they are flagged as debris.
Decals stay behind
Blood decals created by barnacles will not be removed when a portal is placed on the decal. This is more related to decals themselves just not moving, rather than a barnacle specific issue.
Disappearing Barnacle
In Black Mesa barnacles become invisible if the player gets stuck on something while getting reeled in. However, they can still be killed. Not in 
Black Mesa 2012 (Mod).
Incorrect tongue placement
The barnacle's tongue clips through the camera instead of being placed off to the side like in Half-Life 2.
TongueTipUpdated spam
For some reason, the TongueTipUpdated input fires every 0.01 seconds.
Pulling is broken
Sometimes the barnacle will grab a player, but not reel them in for a few seconds, until it catches up and pulls the player faster than usual.
This does not seem to happen in Black Mesa 2012 (Mod).
Grabbed NPCs disappear if barnacle dies
NPCs that are grabbed by a barnacle will immediately disappear when the barnacle that grabbed it dies.
This does not seem to happen in Half-Life 2 and Black Mesa 2012 (Mod).
Eating Headcrab Only
Barnacles in Half-Life 2 will eat the whole zombie NPC, while in Black Mesa 2012 (Mod) the headcrab is ripped off the head. This does not depend on the type of zombie, it works with any zombie type.
Class hierarchy
Portal
Workaround:Fix the model or make barnacle friendly to npc_rocket_turret.
