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Discussing variety of enemies and their abilities in Field Intensity. Beware of spoilers!

Posted by on - Basic Design/Concepts

Field Intensity has a quite diverse bestiary of enemies. Most of them are well-known monsters from Half-Life and Opposing Force, but once we switched to the custom game libraries, we got to add even more stuff upon that. And not only new enemies, but also new abilities for existing ones.

Note: SPOILER AHEAD. Don't read this article if you haven't played the mod yet!

Vortigaunts (aka Alien Slaves)


Personally, vortigaunts are my favorite creatures from the Half-Life series. We've got to know a lot about them from Half-Life 2 and episodes, but even before they looked quite interesting. Being a vortigaunt fan, I've added a lot of new features and abilities for them in Field Intensity to make them more threatening and challenging.

  • When a vortigaunt is idle, they play some electro sounds and visual effects. It's a cut feature from Half-Life I stumbled upon looking at the source code and I've never seen anyone restore it in the mods. This is not the most interesting one, so let's move on.
  • Vortigaunts can resurrect dead comrades. It's another cut feature and you could see it implemented in Sven Co-op. In Field Intensity however the vorts can revive only if the game is played on the hard difficulty, and each vort can be revived only once. This ability also requires a resurrector to have something that I've called "free energy" or "spare energy". More about it below.
  • Vortigaunts restore health when zapping the enemies. The idea is taken from the Half-Life: Decay bonus mission. And there's another concept on top of that. If vortigaunt is already at full health when performing the lightning attack, they get a portion of spare energy which they can spend on some other abilities (like reviving). You can think of it as mana from the RPG genre.
  • Vortigaunts can heal their comrades. This is rarely observed, but vortigaunts will zap their wounded brothers if they can't reach the enemy with their lightning attack or when there's no enemy at all. Just like reviving, it requires some "spare energy".
  • Vortigaunts are capable of a coil attack. When a vortigaunt is surrounded by multiple enemies or if the enemy got too close during the charge, the vort will emit a deadly wave around him, kinda like houndeyes do. It's a nod to the "takedown" attack introduced in Half-Life 2: Episode 2.
  • Vortigaunts may use amplified melee attacks. If a vortigaunt has some "spare energy", their claws glow during the melee attack and deal more damage.
  • Vortigaunts are able to spawn snarks. In Field Intensity this behavior can be observed only on Xen levels in the chapter "The Verge".


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Bullsquids got an alternative projectile attack: a big slow poisonous ball. The new attack type is available only on medium and hard difficulties. It's one of rare examples when the difficulty affects not only the monster's basic parameters like the amount of health or the damage they deal, but also their behavior and abilities. I think we should strive for that more in mods and games. In Half-Life female assassins can turn invisible only on high difficulty and it's a really neat detail.

Mutated snarks

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Actually I should have mentioned them in the article dedicated to weapons, but I completely forgot! Anyways, snarks are both weapons and monsters, so they fit in this article too. The interesting part of mutated snarks is the historical background that led to introducing these creatures in the mod. I've already mentioned in previous articles that Field Intensity started as an Opposing Force based mod. But every mod-maker wants to add something new in their project even if they don't use a custom game code. And Opposing Force had a weapon that was not presented in the singleplayer campaign: penguins! This absurd weapon was introduced with CTF update and worked just like regular snarks except for its increased explosiveness. Taking into account that snarks are hostile against Gargantua which is vulnerable to the limited types of damage, including explosives, the idea of using penguins against this giant creature came naturally. Of course we couldn't leave their appearance as is, so the model was changed to recoloured snarks. When we switched from opfor to our own game libraries, we still kept the idea of having explosive snarks, and the visuals of explosion were updated to more organic ones instead of regular explosion effect.

Baby gargs


Gargantuas are fun enemies, but their size, resistance to bullets and the level of danger they pose don't let a mod-maker throw gargs at a player's face too often. Introducing baby gargs in Sven Co-op was a nice solution, and we always wanted to have them in our mod too. Having the custom game libraries allowed us to add these enemies in Field Intensity.



Floater is a cut creature from Half-Life. The idea of adding them in Field Intensity came from a desire to have flying enemies at some point. We couldn't use alien controllers freely as they seem to visit Earth only on special occasions like opening a portal in Lambda Complex or re-engaging the dampening fields in Decay (Field Intensity, however, still violates this rule once in the chapter "Hazardous Environment"). Floaters were implemented as simple as "kamikazes" that fly into the enemies and blow up at close proximity. While there're known examples of using suicide as a defensive strategy among swarm animals in nature (e.g. honey bees), I still feel like this is not the best approach as we already have similarly working creatures in Half-Life (snarks), and I'm eager to see a proper implementation of floaters in some other mod: they definitely deserve better! Anyways, taking into account the swarming nature of floaters we also showed them in a calm state: in the chapter "The Verge" floaters fly peacefully between the water sources and some kind of sockets in the caves.



Another cut creature, a kingpin has been exciting the minds of Half-Life fans for years. Possessing psionic abilities, a kingpin opens a lot of opportunities for mod-makers. However only a few mods implemented him into a real enemy. The known examples are Sweet Half-Life and Sven Co-op. Having a portable medkit and babygarg in the mod, it made sense to stick to the Sven Co-op concepts. I believe kingpin was a nice addition to the mod working both as a boss and a scripted scene actor.



Yet another cut enemy from Half-Life. Panthereyes exist only as scripted monsters in Field Intensity. While we could have implemented them into real enemies, there was no place left for the battle encounter with these creatures in the latter stages of the development. We might introduce panthereyes in some future project.

Zap traps


While these are not creatures, zap traps pose a threat to the player, so they can be called enemies in some way. When a player comes close to the zap trap it starts playing a warning sound and if the player stays in the range, the zappy ball leaves its socket and targets the player. Its behavior and visuals are the same as the homing projectile of an alien controller.
The idea of the zap traps field comes from minefields in Half-Life, shown in the chapter "Surface Tension". Unlike mines, however, zap traps can be placed on walls and ceilings too.
You might notice that Field Intensity also utilizes another idea from Half-Life - a puzzle with a laser, again, reshaped into its Xen variant.

For me, working on monsters' AI was the most fun part of programming for Field Intensity. And I hope you liked the results.


I really liked your implementation of the Floaters. It was a great fit in the Xen levels.

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Yep, and the changed behavior of the slaves and bullsquids added quite a challenge even to seasoned HL-veterans who are used to the attack patterns for decades.

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This is the best mod of all time and I can't imagine just how much love was put into it. You rock!

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This is the coolest mod I've seen lately, you paid so much attention to the NPCs it's cool, I liked the way you improved the vortigaunts the most.

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Great job! Still, it's a pity that panthereye has not been implemented. We have it as a boss in Azure Sheep, so it even could be taken from there, maybe with some cool additions. Also, I'd wish to see more changes to behavior of other common monsters, like it has been done to vorts.

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