Q&A: Building and balancing Battletech's procedural missions

Fitting procedurally-generated elements into an RPG means walking a tightrope of careful balancing and tuning, a task that’s made even more challenging when the RPG in question is as nuanced and complex as Battletech.

It makes sense, then, that lead designer Kiva Maginn and the team at Harebrained Schemes attacked generating content for the recently-released strategy game in a layered, complicated way. 

Procedurally-generated missions weren't actually a core part of the Battletech game Harebrained pitched on Kickstarter; they were one of the stretch goals, and when the campaign raised enough money to merit their inclusion, the team had to decide how best to incorporate them into a hand-crafted strategy game with a core storyline.

Gamasutra recently reached out to Maginn to hear more about how she and her compatriots implemented a procedurally-generated mission system that can reliably present players with a believable setup and, perhaps more importantly, an interesting challenge.

Her answers were so fascinating (and so detailed) that we thought you might enjoy reading them for yourself, in full, below.

How are the game's side missions designed/generated? How much of the content in them is set, and how much is procedural?

Maginn: The procedural missions are built out of three layers. At the bottom layer is the map itself. Maps are hand-created by a designer, using assets created for us by the environment art team, and tools built by our technical art team. Then the environment artists go back over the map and polish it, adding details, filling out areas, sticking rocks all over everything, and so forth. The maps are intended to be large enough that we can stage several encounters on a map without you realizing it’s the same place, and there are some additional mechanics that allow us to switch what structures, facilities, roads, and so forth are on the map on a per-encounter basis.

The middle layer is the encounter. It’s a generic, flavor-free mission, one of eight types. We’ve tried to capture what we think are the most common scenarios in a BattleTech context -- a straight-up battle, a convoy ambush, a targeted assassination, and so forth. All the logic and scripting that makes an encounter work is embedded in the generic version. Designers then use the Unity prefab system to stick copies of the encounter and all its fiddly bits onto the maps. We move spawn points around, drag patrol paths into place, and generally get the encounter properly set up for the terrain it’s going to be on.

The final layer is the contract. A contract contains all the flavor bits that aren’t part of the raw mechanics of the encounter. So if you’re blowing up a warehouse full of weapons, that information is in the contract layer. The encounter just knows this is a mission where you’re going to destroy a base; it’s the contract that supplies the text to describe it as a weapons warehouse. Contracts are aware of the encounter they’re written for, so they map directly onto all the mechanics of the specific encounter; that is, if the encounter calls for two groups of enemies to spawn, the contract must specify what’s in those two groups.

The nice thing is, while maps and encounters are all part of the Unity scenes, the contracts are a JSON layer over the top of that, so they can be built and edited in a text editor. On top of that, I wrote a simple markup language to make contract creation even simpler, and that markup is parsed into the actual JSON the game uses. So we can rapidly create and iterate contracts, and (maybe most importantly) diff them against each other in git.

When you go to take a procedural mission in game, the game looks at the star system you’re in to figure out what maps are available. If it’s a frozen ice world, it’s going to look for an arctic or tundra map; if it’s a desert world, it will look for a desert or wasteland map. Then it looks at all the encounters on that map, and picks one. Then it looks at all the contracts that fit that encounter, and checks to see if you meet the contract’s requirements -- difficulty, reputation, and so forth -- and then picks one. It also looks at the possible employers and targets in that star system, and picks one of each for the contract.

I think the best way to describe the entire process is ‘procedurally generated from hand-created, curated parts’.

How do you balance the side content to be appropriate for the player's power level, without knowing specifically what the structure of their lance looks like?  How do you use main story progression to throttle player progression? 

Trying to figure out how strong a lance is turns out to be the great white whale of BattleTech design problems. There have been multiple different Battle Value metrics, with lots of complexity behind their valuations, but nothing has ever really been comprehensive. Our solution was, largely, to stop trying to understand the strength of a lance, and instead focus on what resources we expect you to have available.

There are two ways we control the overall player power and challenge level: the global difficulty, and travel restrictions. Global difficulty is a value from 1 to 10 that indicates how heavy the enemy ‘Mechs you face are likely to be. We’ve got over a hundred different lance definitions, each one rated by its difficulty, and each one specifying the weight and role of its members. When we spin up a new mission, we decide what enemies to spawn by taking the global difficulty and finding a lance that matches that difficulty. There’s a bit more complexity there, as the contract is allowed to modify the difficulty before it goes looking for a lance to fit, but that’s the basic structure.

The difficulty ticks up at specific events throughout the story, so that as you progress you face harder opponents. The way we handle loot, though, means that an increase in difficulty also means an increase in player power. If you meet a heavier ‘Mech than you’re used to, you have a good chance of being able to salvage it for yourself. So when we tick the difficulty up, we’re also expecting you to grow to meet that difficulty.

At the same time, we give you a fair bit of control over how tough you want your fights to be. Each star system has its own difficulty adjustment; some places are nastier than others. You can always fall back to easier locations if you’re getting overwhelmed by the battles, or push into harder hotspots to up the challenge. Additionally, when contracts are generated, we vary the difficulty by -1 to +1, giving you a range of possible battles even within a single system. If you’re getting stomped and need some recovery time while you send out the B-team, you can probably find an easier challenge.

None of this is perfect, of course, and you can still be surprised by a much harder or much easier mission than what you were expecting. That’s just part of the nature of procedural content, and of the kind of simulation we’re shooting for. If you realize you aren’t going to be able to make a profit off the mission you’re on, you can always retreat -- and if you’ve made a reasonable effort, you will still get paid for your attempt. One of the mantras we’ve repeated throughout the design process is ‘we want you to run away’, and the potential variance in contract difficulty feeds into that mantra.

That said, there are difficulty spikes and troughs that push a bit too far, into territory we consider potentially unfair, and so we’ve started addressing those on a contract-by-contract basis. Sometimes we meant for you to be fighting a tough ‘Mech, but other times we’re asking a mid-game player to fight an Atlas, and that’s just not fair. This is fallout from the way contracts layer onto encounters. The encounter might offer three different ‘ambush’ lances for the contract author to enable or disable. But if the contract author enables all three, she’s going to be asking the player to fight 12 enemies simultaneously. On some maps, this might be reasonable; maybe there’s a choke point, or some high ground with cover. But the contract author doesn’t know that; the encounter might be implemented on a lunar map that’s just a big open space with no cover and no way to cool off your ‘Mechs. That’s a death sentence.

So there’s a lot of moving parts in the difficulty mechanics, and the target isn’t perfect matching of difficulty to player power, but rather ballpark matching, with the assumption that the player can escape a bad situation by withdrawing, or prevent a bad situation by choosing slightly easier missions.

I mentioned travel restrictions, but that actually has more to do with a later question, so I’ll talk about it there instead.

Can you give me any specific examples that came up during development, play-testing, or during the beta of something that broke the balance you were looking for and prompted you to change the design of the side content?

The biggest challenge has been matching the difficulty progression in procedural content to the difficulty progression of the story. On one hand, we need to get you prepared for the story mission, which means we need to provide you with ‘Mechs we believe are capable of beating the mission. On the other hand, we want story missions to be major, memorable challenges, with enemies and situations you haven’t seen before and higher stakes than previous procedural content.

There’s a mission about a third of the way through the campaign where you have to stop a Union dropship from taking off. Based on what we expected the player to have available at that point in the game, I built the strongest lance I could -- with the rule that I could only use Medium ‘Mechs. We couldn’t be certain the player would have Heavies at that point, and I wanted to find out if the mission was winnable without them.

I got stomped into a pile of scrap. It wasn’t even close. I went back to the drawing board, trying a few different ‘Mech configurations, seeing if knowing the mission and building for that knowledge would make the difference. It didn’t; I failed three times in a row.

Based on that experience, we had two options: we could make the mission easier, or we could make the player more powerful. We opted for the former, because I really didn’t want to cross the line into heavy ‘Mechs that early in the game. We tweaked the difficulty down iteratively, making small changes and then trying the mission again with different Medium-only lances, until we reached a point where I could consistently win and not lose any ‘Mechs.

As an aside, I consider ‘Mech loss to be effectively a failure. Once you lose a ‘Mech, assuming it’s of a reasonable size for the mission you’re on, you may not be breaking even on the mission any longer. So our tuning target isn’t ‘win the mission’, because winning with only one ‘Mech left standing on the field isn’t really winning at all. Our target is instead ‘with clever play and a little luck, win the mission without losing a single ‘Mech’. I’ve staggered across the finish line with missing arms, missing legs, and pilots turned to jelly by repeated knockdowns, but the metric is always economic: did I make money, or did I lose money?

How do the management systems like the store and ship upgrades play into that balance?

Stores are interesting because their contents are so random. This is where travel restrictions come in. When you start, you only have access to four systems, and we’ve intentionally made those systems utter garbage. They have bad shops, they have bad contracts, and they have very low difficulty. While you can make progress there (there’s a Reddit user who played in those four systems for 10 years of in-game time, which is simply astonishing to me) they’re designed to push you into the story as soon as possible.

After that you have access to many more systems, and those systems can contain weapons and ‘Mechs you haven’t seen yet, but there are no guarantees anything will be at a specific store on a specific planet. Only the absolute basics -- ammunition, heat sinks, and so forth -- are guaranteed to be available. Everything else is chance, though it’s chance you can manipulate somewhat. High-tech systems have a higher chance of interesting gear; industrial systems do as well. Poor, backwater systems with no industry other than subsistence farming are very unlikely to ever have weapons or ‘Mechs you’ll want in their shops.

Still, this means that there’s the potential for discontinuity in the difficulty curve. You might find an AC/20+++, the single most damaging weapon in the entire game, before you even dig into the main plot. Our approach to this kind of discontinuity is, essentially, to shrug. Buying and using that weapon is going to be a leg up on the content. It’s going to make you feel powerful, and it’s going to give you amazing moments of utter destruction. But in the long run, one weapon, or one ‘Mech, or one pilot isn’t going to overwhelm the game’s difficulty curve. The name of the game in Battletech is ‘ablative resource management’. You’re losing stuff constantly. Your gear is blowing up, your ‘Mechs are falling over, Dekker is dying, and you’re having to play catch-up constantly.

This is best exemplified in a mid-game mission where we make a very powerful weapon available to you. Every time a player acquires this weapon, they’ve basically gotten a dilemma in a box: if you take this out and use it, sooner or later someone will get lucky and shoot it off your ‘Mech. If you don’t take it out and use it, it’s worthless to you. What do you do?

Ship upgrades, on the other hand, are forever. There’s basically two things ship upgrades do for you in terms of mitigating difficulty. The Mech Bay gets your ‘Mechs working again, and the Med Bay gets your pilots working again.

People are often astonished when they first come out of a battle where a MechWarrior took a single injury, and see that she’s going to be in the hospital for a month. Those healing times are the result of a lot of tuning and re-tuning and playtesting and feedback. The balance we’re looking for is that you can have favorite characters who stay with you through the whole campaign, but at the same time you can’t only have your A-team. You have to diversify, hire some rookies, and get them trained up as best you’re able. What we want to see is: you’re forced, by your budget, to take a contract when your best pilots are in the hospital and your best ‘Mechs are out for repairs.

Upgrading the Argo means that your people come out of the hospital faster, your ‘Mechs come out of repairs faster. So those are just strictly reducing the difficulty of the game, by giving you access to your peak power level more frequently. To compensate, they’re brutally expensive. The target is that you’ll spend roughly the same on maintaining those facilities as the opportunity cost of the extra mission you might not have been able to take without them.

The management sim, overall, gives context to the game’s difficulty and gives you reasons to push into harder content or pull back into easier content. It’s also the enemy for our tuning efforts, because it’s so big and so complicated and the player can use it in so many different ways, unpredictable ways, and potentially trivialize content we expected to be difficult.

One of my defining gaming moments was playing Dark Forces 2, which is the first of the Star Wars FPS games to give you access to Force powers. They let you decide for yourself what you’d learn, but this meant that the content had to be built without the expectation that you’d have any particular power. So you couldn’t have jumping puzzles that required Force Jump, because the player might not have learned that yet. As a consequence, if you did have it, you could easily bypass all the jumping puzzles.

This was fantastic and I loved it. Too often, games offer you the chance to become powerful, and then instantly scale up the challenge to precisely compensate for your new powers. The classic example is to give the player a fireball spell and then immediately introduce enemies that are immune to fire.

What we’re doing, by throwing open the management layer of the game to the players, with all its potential exploits and power-ups and emergent uses, is letting them learn the really amazing Force power and then use that power to stomp all over the game for a while. That feeling of satisfaction from completely overwhelming an enemy is the payoff for all the missions where you’re struggling to stay alive, limping towards the evacuation zone, and trying to hold in your ‘Mech’s innards.

You’re commanding 15-meter-tall walking tanks with massive guns and fists. We want you to get the chance to feel like a complete badass.