With the success of XCOM's relaunch back in 2012, a number of game developers have been looking to take their own stab at the turn-based strategy formula, resulting in the surprising success of Mario + Rabbids: Kingdom Battle in 2017, and in 2018, the release of Mutant: Year Zero right before the holidays kicked off.

Thanks in no part to a foul-mouthed talking duck, Mutant: Year Zero has managed to find an audience and a strong niche in the strategy game space, showing how even a stripped-back version of XCOM can do well with the right tone and sense of polish. We've been enjoying the game over at Gamasutra, and were excited a few weeks back when game director Lee Varley, designer and studio founder David Skarin, and lead animator Calle Granstrom took the time to talk about their work over on the GDC Twitch channel.

There were a few key insights from the trio about Mutant Year Zero's design and game balance, so we took the time to collect a (lightly edited) transcription of their most salient points. Read on for a look at how a bunch of Hitman veterans managed to make their own strategy game.

Adding stealth to the XCOM formula

Skarin: Quite early on, from almost day one, we made the decision that we wanted to keep the stealth aspect as simple as we possibly could. The reason for that was we didn’t want the players spending any more time there than we needed to tell the story and let you explore the world. Because what we wanted to do was to do the stealth moments, or you know set up for combat, while you’re in real time so we could speed it up a little bit but if we started adding too much functionality to that it would just slow it down again right?

So we made a decision very early on that we wanted to keep the amount of game mechanics that you can utilize in the real time to the minimum, and keep it very very simple. So that’s shown for instance in the attention circles that we use rather than any vision cones or anything like that. We didn’t want people trying to sneak on a corner too much or spending time doing that.

Skarin: Yeah, exactly that was the choice. It was either that or giving them, whenever you get discovered, you get a little leeway time. As we would’ve done in Hitman for instance, the guy would’ve come over and investigate, but like it was other problems right for balancing the game? So that was quite early of a decision that we don’t put anything extra that we didn’t need into the real time. And as you can see, the attention circles here now, as long as you stay out of them you have the advantage, right? And that communicates very very clearly.

The idea [with the awareness zones that glow red as you approach] was that this should be a tense moment but that you shouldn’t feel stressed about it, so to speak. You should feel like you have the time to check out the guy coming in on a patrol here and see what’s behind him, etcetera, before setting up. If it were vision cone based for instance, that vision cone might just “BAM” come all of a sudden as he steps from behind a building or a car or something.

Granstrom: We didn’t want to make it something to skill based, basically, when you sneak around it should be more about making a tactical decision rather than being stressed and making quick decisions.

Varley: It was always a design that we wanted the stealth to not be twitch gameplay, because the game isn’t twitch gameplay at all, the game is very much about planning and making good tactical decisions. So the stealth had to feel like it was feeding that quite well. So the stealth in this game is much more about you finding good positions, and working out ‘maybe there’s someone who’s isolated that I can pull down without anyone else seeing.’

The very start of the game that you’re just seeing now is very much designed to be a general introduction to stealth. So extremely obvious patrols of guys with low health walking around on their own, it’s not very taxing, it’s not very challenging. And the characters when they talk they’ heavily hinting at least 2 or 3 times that we should investigate who’s here and we should sneak around first. So I would say that the first 20 minutes of the game is gently pushing the player into this kind of playstyle, rather than us hitting them with a hammer, if that makes sense.

Skarin: In user research about a month ago or something, it was one of the things we probably didn’t communicate enough. We have added some tutorial messages around this. Because if you don’t figure it out rather quickly, the levels can become quite hard later down the line. Because we really wanted you to scout out these positions. You don’t always have to pick off everybody around the map, but at least figure out that they’re there or, when more advanced units step into the zone that can help other units and such, it’s very important that you know about these units or they will surprise you.

Varley: It was also important that the stealth doesn’t become boring in the game. Because this pattern [in the start of the game,] you repeat that too much it’ll start to get stale. So in the game’s balancing, the enemies that get harder the further in the zone you get, and the enemies health will slowly start to track ahead of your stealth weapons. So at some point in the game you’re going to start having to use multiple characters with stealth weapons to kill an enemy, or make use of your mutations that allow you to do double damage or crit damage and stuff like that to be able to pull off a stealth kill.

Skarin: So it’s actually, now you’re out of combat, but we have a critical hit and a regular one and that was the balance you were talking about. It’s kind of in layers, that balance, it’s quite nice, where during the mid-game you have to start doing critical hits with your silent weapons in order to take these straggling characters out, or these outliers, so it becomes a little bit deeper to do it which is quite nice. And towards the end, yeah you’ll have to use basically all the tricks in the book if you want to take anybody out on the outskirts.

Why game designers need to lie about hit percentages

Skarin: First of all of course we’re also cheating behind the scenes, because people don’t understand percentages very well. So a 75 percent shot here is a bit higher, right. We’ll also do a few tricks on the AI side where if they hit you they’ll actually have less chance next time and such so you don’t get into these streaks of the enemy feeling super powerful just because they got a lucky run. you need to do a couple of these things, specifically around 50 percent, right?

You shouldn’t be taking those shots really. You shouldn't be taking 25 percent shots in an XCOM game really. People expect four 25 percent shots to be a hit. So one way of doing that then of course is to add a bit when you miss. So we have a few of those tricks going on behind the scenes, but I think it doesn’t deter anything from the game. We added more along the lines of we felt it was needed. It’s better that the game feels fair, than that it is fair.

Varley: Especially the hardest thing to do in these games is to make them feel fair.

Skarin: Yeah, and Lee was also very early on with [defining] the percentages. We looked at Mario + Rabbids I think.

Varley: Yeah, they do 100 and 50 which is more extreme than we are.

Skarin: But we went with a system in between.

Varley: Yeah, we went for like an in-between system where we round the numbers up to the nearest 25 percent I think it is. Because it just feels a bit more, for me personally when I’m playing, it feels a bit more easier to predict what’s going to happen. A 75 percent to me feels not guaranteed, it’s still a bit of a gamble. 50 percent, feels like, we know what 50/50 is, its a complete gamble. 25, that just feels like it’s going to miss. Whereas if I’m playing and I get a 87 percent chance to hit that’s a little bit more difficult for me to get a feel of what that number means to me. if i’m taking my shot.

Skarin: What we did was we basically said oh your bonuses are on a 25 percent, so a low cover will give you 25 percent while a high cover will give you 50, like that kind of stepping instead of going with 10 percent or you know some certain angle, trying to be a little more binary so that players will learn that ok i’m going to take 75 percent shots or try to get 100 because in our game it’s quite easy to get 100.

As long as you flank an enemy you’ll most likely be getting it. we do have range in there, but that’s what we wanted. we wanted players to figure out how to get 75 or 100 shots every time, right. And then try to be pretty harsh on the other ends so you know. I’d rather give you 0 percent than 5 percent, so to speak, because we don’t want you taking 5 percent shots anyway.

Varley: Yeah, it was like to try and make the game feel a lot more fair. Where we want to we reward players for doing good tactical moves a lot more than other tactical games will do. So if I pull off a really really good tactical move and I’m flanking someone, but then I only get an 82 percent chance to hit and I miss, it doesn’t feel like I’m being rewarded for doing some good tactical play. So in our game if you do a good tactical play, you do some good positioning, which the stealth is directly feeding into that, then you’ll be rewarded pretty highly.

Skarin: It is a tricky one, that we haven’t solved completely here, which is teaching players what flanking means. because it’s the same rules as XCOM uses which basically means that you need to be on the same, behind the grid point that the cover is on, but because we have very lush environments that look almost biological at times, it can be really hard to communicate that. And we opted to go for the, you’ll see if you switch to combat here, making sure that we show the line of fire and the count of your percentages to all the characters in a preview from any tile that you want to move to and that way you can kind of explore where you would get the best advantage. I’m not sure what’s in this demo actually because we’ve been adding a lot lately, but let’s see when you get into combat.

How I learned to stop worrying and love Microsoft Excel

Varley: [Balancing Mutant Year Zero] is difficult to explain. Just a lot of playtesting, that’s all you can do. this map that you’re seeing right now I must have played this a thousand times. And every time I play I adjust the cover around, and then I play again, and then I’m like this would be so much better if I had a cover here, and then I adjust the cover around, and just keep doing that process over and over again.

Skarin: Yeah, I remember when we generated trees for instance at some point we had a distance we wanted to put them so you could always get in cover, but that doesn’t work to make for an inserting space in itself, so I think that yeah there’s no shortcut there. You really have to play it. I mean there are some ground rules you learn after a while, that you know, you need to have four tiles between high cover walls and buildings and such.

Varley: Sometimes it’s fun to remove cover from the area as well, so the player has to make completely different decisions. Maybe they have to make a sprint move to get to the good cover on the other side. The only real way to do that is through just a lot of playtesting.

Skarin: That it is a large game to balance.

Granstrom: Yeah. It’s the hardest game I’ve ever done.

Skarin: Yeah, I mean, it’s about 15 hours of gameplay even for us that know the game very well. And of course, we, like we discussed earlier, we changed the balance for the stealth for one, like how many units you can take out, and then you can take them out if you use the correct strategies, so lots of lots of balancing and really really tricky to balance the whole way because of the amount of time that it takes.

Varley: I think, one of the big things that have hit us from the public demo that went out was the response. It’s taken me by surprise how much people are enjoying the game. because we’re completely close to the game so we can’t see it anymore. we’re completely blind to it. There’s the old saying with game developers: we only do with problems. That’s how our entire day is, just problems all day long. We never take a step back to go “oh wait a minute we’re actually building something people really like. “

Skarin: Yeah, it was for balancing, because we get two completely different answers from two different people, right? We have Rui Casais the CEO of Funcom and he’s a really hardcore XCOM fan and he’s constantly been telling us to make it harder and harder and harder. And we have the people that are not hardcore XCOM players and they’re like its way too hard its way too hard. and then you have, because we went with this option where you can take people out silently, that became another one. not just balancing a fight, but if you don’t take anybody out that fight will become way too hard. But if you take as many as possible out it’ll be too easy. So that’s been a tricky one.

Varley: A top tip for any game designers out there, stick all your numbers in a big Excel sheet and make some formulas in there, so if you change one number somewhere you can see what it does to the rest of the game. that’s my approach with this and that’s the only way I’ve been able to get on top of it I would say. If I change how much damage the crossbow does over here I can see roughly what it does to the end game.

Skarin: We’ve finally become old enough to praise Excel. I think that was probably the biggest thing we went thru during the beta period now was just how large the game was. It’s always hard to say how many gameplay hours you have as well, of course, early on and we were playing this in different segments calling it like it would, the start of the game the mid game, the end game, and were just playing those segments but never doing that full run. you wanna do it as early as possible, we always do it too late. and in our case it meant we had a lot of hours to balance all of a sudden. so maybe we should’ve… I don’t know what we should’ve changed to be honest, it’s just a large game.