Poison Zombies are one of Half Life 2’s most mechanically unusual enemies: not in terms of how they’re supposed to be beaten, but how they fight and the kind of threat they can pose to a player. While a regular Zombie might be able to hound the player in a certain direction or serve as an additional threat to avoid during platforming or puzzle segments, a Poison Zombie is capable of delivering instant death to the player in the right circumstances, and can perform a limited amount of area denial and player harassment from a distance.
The Poison Zombie As An NPC
Poison Zombies behave similarly to standard zombies while idle – they wander around aimlessly, search for new threats and make feral grumbles and groans. While all Zombies sound somewhat terrifying, the Poison variety have a special set of sounds that emulate the grunting and groaning of a dying, crying and poisoned old man. Lovely.
Most of the general AI behaviour is still the same, right down to way they navigate the world. If you want to get an overview of how zombies work, you can check their entity profile here. Any techniques that work with regular Zombies will work for them, too, so they’re generally the same in terms of mobility and how they approach their targets. However, they deal far more damage than the standard variety, often approaching (or even passing) triple their normal damage output per swing. On the other hand, their swings are far less common and frequent, and they attack at a much slower rate than the standard variety, making them weaker overall in terms of their damage per second.
The Posion Zombie has a unique attack that can easily catch first-time players off guard – the ability to throw up to three Poison Headcrabs at their targets from a distance. This isn’t just a way to damage the player like a standard ranged weapon – these Headcrabs become a separate NPC entirely (which will get covered in more detail in a future Entity Profile). Like any Poison Headcrab, they’ll instantly reduce the player’s health to 1 on a direct hit, followed by the player automatically regenerating it – minus ten health from the total they originally had. This can’t kill the player on it’s own, but it opens up an opportunity for the Poison Zombie to deliver a killing blow.
As with regular Zombies, the Poison variety can also drop it’s main Headcrab if it’s killed without sufficient damage to the head, as well as any remaining Headcrabs on it’s back. This is much more common than the main one dropping, even if the Poison Zombie is hit with a direct explosion, but fire and vaporization will usually take them all out at once. However, they can’t survive any kind of bisection: they’re either alive or dead, with no crawling version. In addition, they don’t have the ability to “sleep” and are much more limited in terms of scripted sequences, so they’re better suited as an actual threat rather than an actor for carefully-prepared background events.
The Poison Zombie As An Entity
Like normal Zombies, Poison Zombies are fairly limited in terms of their entity properties and Flags. The only major option that’s unique to this variant is the “Crabs in nest” setting, which adjusts how many Poison Headcrabs it carries on it’s back, with a maximum of three and a minimum of one. This does not include the one controlling it, meaning that you’ll be choosing between four and two Headcrabs in total. As mentioned before, the ones on the back have a very high chance of dropping off if they haven’t already been thrown, so you should set it to the lowest possible value if you want to give players an easier time.
Other than that, they have no special Inputs or Outputs with other entities and triggers aside from the ones shared with most NPCs. The way they handle navigation is also similar, with the ranged attack being the only difference: it’s triggered seemingly at random as long as the player isn’t in (or very close to) melee range, and the throw is angled in a way that will send the Poison Headcrab directly at the player. If they’re in an unreachable spot, the Poison Zombie will usually throw the Headcrabs repeatedly without pause until they run out.
The Poison Zombie As A Level Design Element
Posion Zombies are one of the most durable humanoid enemies in the entire game, with over triple the health of a Regular zombie and an immunity to bisections from explosions or sharp objects. Even if they’re shot in the head, it can take multiple magnum rounds or two RPG direct rockets to take them down properly, making them an extremely important threat that many players will try to take out as quickly as possible. They’re perfect for a “tank” role, acting as a slowly-approaching bullet-absorbing obstacle that can back poorly-equipped players into a corner: they aren’t particularly fast and they have limited ranged attacks, but one or two Poison Zombies can put a lot of pressure on player without many weapons.
Their ability to deploy Poison Headcrabs also gives them a certain level of area denial, since they’re more likely to throw them if the player is far away or on a surface they can’t reach. This makes it incredibly hard for a player to just hide on a raised rooftop of object, and can harass the player into changing positions where they’re more exposed. While no amount of Poison Headcrabs can actually kill the player, they can still wear down their valuable health straight through whatever shields their HEV suit has.
The instant reduction to 1 health point also means that even the smallest type of damage can immediately kill them. If a Poison Zombie gets a chance to drop one or more of it’s Headcrabs, they can work together to instantly kill the player under the right circumstances. However, this means that they can also be ranged support for other Zombies: if the player’s getting pursued by a crowd of the regular variety, a single bite of a Poison Headcrab can temporarily make the fight much more weighted against them.
Each Headcrab can also take a while to kill, which is compounded by the fact that they have slightly more health than a standard Headcrab (just under double). Since a single Poison Zombie can be come up to four targets at once (and even sometimes drop it’s own Headcrab when it dies, giving it an extra chance to harm the player), a handful of Poison Zombies can saturate an entire room with extra targets, taking up a lot of the player’s resources if they don’t have another way around. If there’s a shortcut or some alternate path they can take, then this makes for a great natural barricade instead, pushing players to use the environment rather than just force their way through.
When mixed in with normal Zombies, many players will see them as a “commander” and try to take them out first, which you can exploit to draw attention away from other groups of Zombies coming from behind. They have very little setting them apart from normal Zombies once their Headcrabs are thrown, but their darker colours and bulkier, hunched posture mean that they stick out more in crowds.
As with regular Zombies, they’re ideal “filler” to include some challenge and hostility into an area without many enemies, and the threat they pose can make many players stop to fight them, even if it’s not necessary. If the player doesn’t have many offensive options, they’re also a good way to keep players on the move, either by harassing them from a distance in open spaces with Headcrabs or slowly swarming after them in linear areas.
Poison Zombies are a relatively minor threat to a fully-equipped player with a lot of room to move around, but their ability to suddenly deploy tough and health-draining Poison Headcrabs adds a lot of extra lethality to a group of assorted Zombies. If the player doesn’t have the tools and time to take them out quickly, even a single Poison Zombie can deliver a quick kill if they get close enough: a fact that can make players focus on them, even if it’s entirely unnecessary and opens them up to being flanked by a letter enemy.
Even from a distance, they’re not harmless – a thrown Poison Headcrab can spread a Poison Zombie’s presence much further, and they’re much more dangerous than most other enemies when it comes to long-range harassment.