asw_drone is a point entity available in 
Alien Swarm.
A vicious killing machine with bladed limbs and sharp teeth, easily able to tear a man to pieces, even an armoured IAF marine. — swarm.fgd, Alien Swarm SDK
Drones are the most common enemies in the game, serving as the weak, hiveminded grunts of the Swarm's army. They often appear in large groups created by asw_spawner. Drones have several unique behaviors and animations available which change how they're fought in different environments.
Placement Tip:Drones are one of the few NPCs capable of using climb nodes. However, they do not have a downward climbing animation.
In code, it is represented by theCASW_Drone_Advancedclass, defined in theasw_drone_advanced.hfile.
Subclasses
Drones have two "sub-classes" which differ in minor ways:
asw_drone_jumper is a drone capable of jump navigation. trigger_asw_jump can control where they jump.asw_drone_uber is a much stronger drone which moves slower and has a lot more health. 
Note:asw_drone_uber has an unused distinct model, but not in Alien Swarm's retail artstyle.
Keyvalues
- Move Clone
(MoveClone) <targetname>
- If set to an entity name, this alien will match movement with that entity.
BaseSwarmAlien:
- Visible when asleep
(visiblewhenasleep) <boolean>
- If true, this alien will still get drawn even when asleep (useful for aliens you see far below you).
- Start Burrowed
(startburrowed) <boolean> !FGD
- Makes this alien start burrowed. Normally set by
asw_spawner or asw_holdout_spawner.
- Can be ignited by fire
(flammable) <boolean> (only in 
)
- If false, this alien will not be ignited by fire.
- Can be electro stunned by tesla gun
(teslable) <boolean> (only in )
- If true, this alien can be electro stunned by tesla gun.
- Can be frozen
(freezable) <boolean> (only in )
- If true, this alien can be frozen by freeze grenade or turret.
- Can flinch
(flinchable) <boolean> (only in )
- If true, this alien works as usual. If false, the alien doesn't flinch on taken damage.
- Health bonus
(healthbonus) <integer> (only in )
- The amount of health to add to an alien.
- Size scale
(sizescale) <float> (only in )
- The factor used to scale alien size. Don't use 0.
- Run speed scale
(speedscale) <float> (only in )
- The factor used to scale alien run speed. Don't use 0.
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
BaseNPC flags
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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]
Note:This 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.
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Use Ground Checks : [131072]
Inputs
SetMoveClone- Wakes the alien up if the Wait For Script flag was set.
BaseSwarmAlien:
BreakWaitForScript- Wakes the alien up if the Wait For Script flag was set.
BaseNPC inputs
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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.
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Outputs
BaseNPC Outputs
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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Source