5e: Hacking the Game, Horizon Zero Dawn Part I

Way back in the mists of mid-2017 (doesn’t time fly?) I began a series of articles called Hacking the Game: Fallout. Over the course of 11 posts, I outlined the process of modifying the Dungeons & Dragons Fifth Edition ruleset, from initial concepts to mechanical changes, in order to facilitate tabletop roleplaying in the setting of the Fallout video game franchise. That hack eventually evolved into a massive undertaking which produced a 231 page PDF and a wiki version of the rules!

Today I’m starting a similar series, with another popular video game as my inspiration: Horizon Zero Dawn. But I’m doing things in a different order this time. By far the biggest single undertaking in Fifth Edition Fallout‘s life cycle was adapting all the content in the PDF (which at the time was already something like 150 pages) to the wiki. Afterwards, I found updating the wiki to be straightforward, and the wiki to be a useful reference format, while continuing to update the PDF became more and more of a chore. Accordingly, this time I started with the wiki. That means there’s already content available for you to see, right now! In fact, there’s rather a lot of it, enough to start playing immediately. Currently, players can build hunters of one of four tribes (Banuk, Carja, Nora, and Oseram) and up to 5th level. I also have no immediate intention of creating a PDF version of the rules. If there’s demand for it, I might do so as and when I can say that the hack is pretty final.

This time the articles are more of a design diary, explaining why I made various choices after the fact. Referencing content already on the wiki will also make it easier for me to produce these posts as I won’t have to reproduce significant bodies of text and sizable tables.

By the way, I’m calling the hack Horizon Zero Dragons (’cause it’s a Dungeons & Dragons hack but there’s no dragons in it… you get it).

One final thing: a key principle of Fifth Edition Fallout was to reskin rather than rebuild. While some brand new mechanics were absolutely necessary to facilitate the Fallout experience, the core game experience hewed as closely as possible to the Dungeons & Dragons game. This time around, the changes I’m making in the Horizon Zero Dragons hack are considerably more extensive. Some are more necessary than others, but in all cases there is reasoning behind the alteration. I’ll be explaining these changes and why I like them for Horizon Zero Dragons as I go.

Now, on to the content! In the first of this series I’m going to briefly describe the setting for the benefit of any reader who hasn’t played the game (if you haven’t and you get the chance, it comes highly recommended!). I’ll then explore some key things the hack needs to factor in, before moving on to discussing Hunters, Ability Scores, and Hit Points.

A Spoiler-Free Summary of Horizon Zero Dawn 

The world is our world, but the time is a very distant future. Somehow in the intervening years our society disappeared. The humans living in the world belong to primitive tribes. These technologically primitive peoples share their world not just with flesh and blood animals, but also beasts of metal: the machines, robots formed in the shapes similar to animals of past ages. The tribal peoples of the world hunt the machines for salvage and use robotic parts in their crafting: they don’t necessarily understand the science and engineering behind their salvage, but they’ve learned how to apply some of that advanced technology in practical ways that create items more advanced than their society’s overall level might suggest. Previously the machines were quite peaceful and hunting them wasn’t particularly dangerous, but over the last several decades they have become increasingly aggressive and dangerous new machines designed for killing have appeared one after another.

You play as Aloy, who was outcast from the Nora tribe at birth for reasons her father-figure Rost is unable to explain. To find answers she undertakes the Proving, an intense ritual hunt that will grant her the title Brave and the right to rejoin the Nora tribe and get her answer. As events unfold, she is tasked with leaving the lands of the Nora and becomes embroiled in a great conspiracy.

Key Themes and Gameplay Elements of Horizon Zero Dawn

The first thing to consider when hacking a rules system to suit a setting or genre of your choice is what the hack needs to achieve. In the case of a video game world like Horizon Zero Dawn, you’re hacking for fans of the game. They’ll want to insert their own characters into the world as presented by the game. This means ensuring the rules can support thematic elements of the setting and provide mechanical support to capture a feel as similar as possible to the original gameplay experience. With that in mind, here are some things that Horizon Zero Dawn either is or includes that the hack ought to consider:


  • The Hunt! In Horizon Zero Dawn, hunting increasingly larger and more deadly machines is a core feature of the gameplay loop. Furthermore, it’s made pretty apparent that the world has become too dangerous for persons who don’t possess survival and self-defense skills to travel far beyond their settlements. Since the core gameplay experience of both Dungeons & Dragons and Horizon Zero Dawn involves adventure and danger, that means every player character needs to have the skills of a hunter. I’m not saying that other professions don’t exist in the world, and I’m also not saying player characters can’t choose to have some of the competencies associated with those professions. But ultimately, characters need to have the necessary abilities that they can engage with parts of the game players are naturally going to expect when you tell them they’re going to be playing in the world of Horizon Zero Dawn.
  • It’s our future, not a fantasy. This isn’t a world of magic, which means no playable races other than humans, no spellcasting classes, etc. This obviously eliminates most of the base game’s options in one fell swoop, leaving very few choices. Factor in the fact we want every character to be a competent hunter, and the existing class system starts looking like a pretty bad fit for this hack. 
  • Post-apocalyptic. The world is reborn anew from the ashes of an advanced society. Some ruins of that society still exist, introducing an element of exploration and mystery just perfect for a game modeled on Dungeons & Dragons rules. Post-apocalyptic settings often have a scarcity of resources, but that’s not necessarily the case here as the resources are abundant. However, gathering many of them requires effort and danger. In Horizon Zero Dawn, especially in the early game when you’re not swimming in metal shards (the game’s currency), you can often find yourself lacking the resources to craft ammo, potions, and traps you want on hand when undertaking the next quest. So you have to go hunting for them. The hack needs to recreate that loop, implementing a salvage subsystem so that many of the useful crafting items come from machines the player characters kill.
  • Tension between highly advanced and primitive technologies. The society that once existed had access to technology well beyond even our current limits, let alone those of the tribal societies that now call the Earth home. From the point of view of these cultures the machines and the things they’re capable of appear practically supernatural. Meanwhile, although the general level of human technological advancement is fairly rudimentary they have learned to adapt parts from the machines they kill. Thus, the existence of the machines rationalises the fact that the tribes have access to some pretty unusual “mad science” weapons, armour, and other items that are well beyond what would otherwise be reasonable for them to create.

Gameplay Elements

  • Damage Types. Compared to Dungeons & Dragons, Horizon Zero Dawn has a fairly limited palette of damage types which should all be included in the game. This includes impact, laser, fire, freeze, and shock. Other damage types may reasonably exist in the world (for example, there is no thunder/sonic damage in the game, but a scenario absolutely could exist where an advanced technology caused such damage. The hack will focus on the damage types absolutely necessary, but acknowledge that other rarer damage types may exist to allow GMs the freedom to utilise them. 
    • Impact Damage. Impact damage is caused by most weapons (and will therefore replace Bludgeoning, Piercing, and Slashing), as well as explosions. Due to the existence of armour modifications that specifically resist only melee damage or only ranged damage, we can therefore further subdivide impact damage into three: melee impact damage, ranged impact damage, and explosive impact damage. 
    • Tear Damage. This is a special type of damage that doesn’t particularly hurt a machine, but tears components off their body. Depending on the component, this might prevent the machine from using an ability, grant additional salvage, or pull a weapon from the machine that can then be used by the player! This is something that absolutely has to be included, which necessitates the creation of a whole new subsystem. 
    • Elemental Effects. In the video game, fire, freeze, and shock damage build up over time and eventually cause the target to suffer an effect such as catching on fire, being frozen, or briefly paralyzed. The Horizon Zero Dragons hack should account for these special effects on all elemental ammunition types and other sources of elemental damage.
    • Horizon Zero Dawn also includes a damage type called Corruption, but we can exclude it because:
      • The trail left by corrupted creatures is described as acidic, so it would be more useful to include a damage type that covers all kinds of acids, alkalis, and chemical burns. Fifth Edition Fallout includes a chemical damage type to cover these sources, and that seems a good fit here too.
      • Corruption arrows deal no actual damage, and the effect they cause can be classified in Dungeons & Dragons as a condition. 
  • The Focus. Aloy finds a special device, a sort of miniaturised personal computer called a focus. Among other things, it lets her scan machines for weaknesses, detect and follow difficult trails, and find resources and tactically useful objects in the environment. Focuses are pretty rare in the world so player characters don’t necessarily have to have access to them straight away (or at all), but they’ll absolutely want the option! The hack needs to support them.
  • Outfits, Weapons, and other Items. Outfits are the game’s armour, and they often have special defensive abilities. Using the armour table from the base game won’t cut it. Similarly, the hack needs a whole new ranged weapons table, reproducing the various ranged weapon types available in-game. Further, although the only melee weapon Aloy has access to is a spear, we see Carja soldiers with glaives and many other melee weapons could reasonably exist. The melee weapons table will be somewhat speculative, and somewhat slimmer than the base game. Aloy can also buy or craft various potions as well as cool traps, so the hack needs to support those as well.

On the Taxonomy of the D&D Character

A Dungeons & Dragons character is made up of several separate modules that interlock to form a larger whole which interacts with the larger rule set to determine what the character is capable of. These interlocking parts are hierarchical: the hierarchy is fairly flat, but it’s there. You can’t decide on any options from character modules lower in the hierarchy without first making choices higher up the hierarchy. 
The modules will largely be familiar to you: ability scores, race, class, background, and so on. The whole that they make up is the adventurer. The hierarchy looks like this: 
The Taxonomy of an Adventurer

A Matter of Class: or, “We’re all Hunters Here”

Why is this taxonomy relevant to the Horizon Zero Dragons hack? Well, as I’ve noted in my discussion of the key themes and gameplay elements of Horizon Zero Dawn, many of the character modules that normally make up an adventurer should either not be available or are severely limited by the laws of the setting. This has a significant impact on the hierarchy.

Firstly, “adventurer” in Dungeons & Dragons is a broad category describing the role of all player characters in the world they live in. It includes all manner of fantastical archetypes with powers strong enough to survive adventures full of monsters and magic. Whereas, anyone daring enough to be an “adventurer” in the world of Horizon Zero Dawn has to be a human (as only humans exist), has to be able to avoid machines where possible and have a chance of surviving battle with them when stealth fails, and has to be self-sufficient in the wilderness. Therefore, in Horizon Zero Dawn “adventurer” is synonymous with “hunter”. Thus, “Hunter” replaces “Adventurer” at the top of the hierarchy of player character modules.

But “Hunter” could also be said to be a character’s class, right? Conceptually, it’s about the same as a “Ranger”, say. We could have different classes exist below “Hunter” in the hierarchy, as different types of hunter. But how many classes could we include? We already know we can’t use most of the classes that exist in the base game. Not even the ranger is quite right, owing to its use of divine magic. Practically speaking we’re left with the barbarian, the fighter, and the rogue, and only a handful of viable archetypes for each. None of them feel quite right. Furthermore, allowing players to choose from only these three classes doesn’t provide enough choices to ensure significant variation between all player characters in a game.

Instead, I opted to run with that first instinct: Hunter is every character’s “class”, as well as their role within the world. Accordingly, it has to be designed to allow a lot of flexibility, giving lots of choices so that no two hunters in the same party need feel the same!

As a consequence of this, all other decisions you make about your player character become subordinate to being a hunter. Decisions like your tribe (which is somewhat equivalent to the D&D adventurer’s race) become decisions you make while undertaking the process of what D&D would term your class. It’s as though you started making a Fighter and one of your first level class features asked you if you wanted to be a Dwarf Fighter, an Elf Fighter, or so on.

The hierarchy of the Hunter looks like this:

The Taxonomy of a Hunter
As you can see, it’s significantly less complex. Though it may seem a little odd at first, incorporating the various player character modules into the same write-up as the Hunter’s “class” features effectively streamlines the character creation process. You don’t have to go look at multiple chapters, or more than one wiki page: everything you need to do is all in one place.
From the point of view of a designer, having only one “class” has another benefit: while I still refer to D&D’s classes for benchmarking, I don’t have to worry about balancing multiple classes against each other. It doesn’t matter if the Hunter ends up overpowered compared to core classes since it’s not intended to interact with classes that don’t exist in Horizon Zero Dragons: the only thing that matters is the players end up having a fun and sometimes challenging experience.

Backgrounds are a Thing of the Past

You’ll notice that backgrounds have been removed from the hierarchy entirely. This is because I deemed backgrounds an unnecessary part of a Horizon Zero Dragons character. We already know exactly what the character’s background looks like: we have their choice of tribe, and the fact that they’ve been trained from a young age to become a hunter.

Note that the mechanical benefits provided by the base game’s background features are still part of the character in some form or another, absorbed into the Hunter’s features.

Ability Scores 

The six D&D ability scores have frequently been the subject of intense debate among my circle. It’s undeniable that some of the six are more useful than others, except in the case of specific classes that are designed around “weaker” scores. It’s also possible to make any number of fairly sound arguments about why a certain aspect of the rules might be equally or better handled by a different ability than the one it’s currently assigned to. Further, there’s some conceptual overlap between the mental and social abilities. These factors combined lead me to the belief that six abilities may be too many, and the responsibilities of those six scores might be better if divided among fewer abilities. Four, say. That would help ensure that every ability score is fairly important to any character, and reduce if not eliminate confusions about which ability is really best suited to a given task.

Especially in Horizon Zero Dragons, in which magic doesn’t exist and social functions may be considered a secondary concern for many hunters, I feel it’s disadvantageous to use the current model which dilutes the cerebral and social ability functions between three scores. We want the ability options available to players to be as tempting as we can make them in comparison to physical abilities. Reducing down the number of abilities is one way to achieve that. Making sure there are ways to use all abilities in varied situations, such as combat, is another. However, the first method can help with the second: from a design perspective, ensuring that the mental and social abilities are used in varied ways becomes easier if there are less of them to consider.

After due consideration, I decided on the following four ability scores: Might (essentially absorbing Constitution into Strength), Finesse (Dexterity), Acumen (combining Intelligence with portions of Wisdom and Charisma), and Spirit (combining the rest of Wisdom and Charisma’s functions).

The Final Score: Modifiers +1, Scores 0.

It might not have escaped your notice that ability scores in Dungeons & Dragons are practically pointless. They’re essentially vestigial things, there now only because they always have been. What’s important in the current edition of the game is your modifier. About the only time you’ll refer to your score is in the context of either a tie-break situation, such as when you want to quickly assess which of two characters with the same modifier is slightly better than the other and make a declaration without rolling. I don’t deny this is sometimes useful, but in those situations there’s only a 50-50 chance that the comparison will be useful. The other 50% of the time, both characters have the same score.

So why keep ability scores? Other versions of d20 before this have successfully abandoned them (True20, for instance). For Horizon Zero Dragons, I’ve chosen to follow in their footsteps.

Making this change does mean that current methods of generating ability scores don’t work any more. I plumped for the simplest alternative method: assigning an array, which is +2, +1, 0, and -1.


As I mentioned, however, the option to compare abilities for quick tie-breaks can sometimes be useful, though it’s hit and miss in its current form. I think we can add it back in but do it better. What if an ability modifier was further broken into four bands?

If you’ve received education in a system that uses letter grades, you’ll be familiar with the method I chose: As well as having a modifier, each of a character’s abilities is assigned a letter grade out of the following options: A (the best), B, C, and D (the worst). The letter grade helps us decide which of two characters with the exact same modifier has the advantage over the other. To illustrate, imagine that each character that possesses Might +1 took a practical exam to measure exactly how much might they have compared to other characters at their level. Although they all have nearly the same Might for most practical purposes, under rigorous testing conditions it can be shown that some in the exam are just a little bit more mighty than others. The top 25% are given an A grade, the next 25% are given a B grade, and so on. These small differences may not matter in the context of battle, such as hit point damage; they could, however, be a deciding factor in a direct contest of strength like an arm wrestle. Particularly when said contest isn’t significant to the story and you might want to avoid bothering with a roll. When we want to make such comparisons, four variations of each bonus is much better than two: That’s 75% odds that two characters will have different values when we need to compare them!

Four grades pairs really nicely with four abilities, as it gives us a very elegant solution for determining a character’s grades: you get one of each and you choose how they’re arranged among your four abilities. Alternatively, they could be randomly assigned by groups who like some randomness in their character creation.

Hit Points and Stamina Checks

A little while back I posted a variant method of rolling hit points which replaces Hit Dice with a Constitution ability check. I really like this as a default for Horizon Zero Dragons. (substituting Might for Constitution, obviously). Here’s why:

Firstly, and definitely primarily, characters in Horizon Zero Dragons are going to have access to less healing than Dungeons & Dragons characters typically have. Sure, they can buy or craft healing potions, but they don’t have access to convenient curative spellcasting. Additionally, any serious injuries or other consequences of lost hit points (death, for instance!) are a lot more permanent: without magic, there’s no way of undoing such outcomes. Therefore, it makes sense to give hunters an extra buffer, making them tougher in the first place. The stamina check variant generally results in a character getting more hit points than they would otherwise have received using Hit Dice.

Secondly, although Constitution is often less useful than Strength, combining the two into Might creates something of a power stat. A consequence of the stamina check variant is that Constitution, or in this case Might, has less of an impact on your hit points: 0.5 per +1, instead of 1 per +1. The impact is nowhere near enough to change the fact that Might is a great choice for a hunter, but it does decrease the comparative value of Might, if only by a little bit. And as they say, “every little helps”.

Next Time…

That’s it for this installment! Next time, I’m going to explore some more Hunter features, including Proficiencies, Tribes, and more. 

Share your thoughts!

Thanks for following along this far. Let me know what you think about some of these changes, as well as any ideas you might have for further development of the Horizon Zero Dragons hack! Either leave a comment, or reach out on twitter.