Chicago's own NetherRealm Studios is best known for its work on the long-running fighting game series Mortal Kombat, but in the space between Kombat outings the studio has also tried its hand at other projects.

One of those ventures, the 2013 DC Comics tie-in fighting game Injustice: Gods Among Us, seems to have done well enough for the studio that it's now poised to release a sequel next year. But Injustice 2 is interesting from a game developer's perspective because it takes an established fighting game chassis (based upon the Mortal Kombat games) and bolts on an item system that players can use to change the way their characters work.

In brief, players basically get loot drops at the end of every match that they can then choose to equip on characters in their roster (everyone from Aquaman to Wonder Woman), changing those characters' stats. It's not totally unheard for a fighting game to include items that change characters' stats (see Street Fighter x Tekken's "Gems" system) but it is rare, and notoriously tricky to pull off without upsetting the game's balance.

NetherRealm's Adam Urbano served as lead producer on the original Injustice, and he's reprising his role for the sequel. At E3 this week, Urbano chatted with Gamasutra a bit about why, exactly, NetherRealm is making another Injustice game and what he's learned about how to build a balanced, tournament-grade fighting game.

Why are you making Injustice 2? What shortcomings did you see in the first game?

Urbano: One of the things is, we wanted the game to be accessible. We wanted Injustice to be something casual people could jump in and play. Thats why you saw the environments and the interactions and a lot of the one-button things you could do that just looked powerful. Unfortunately, it's extra difficult in just the short amount of time in the [training] mode in Injustice to really get good at things. So the gear system is a fundamental redesign to address things like that.

The goal is that you start out with a much more accessible easier-to-play character, and then you're going to grow with that character, over weeks and weeks and weeks if you choose, giving you a chance to customize it and make it play the way you want it. Actually getting to learn how to play, as well. Instead of just presenting you with 26 or so completed characters from the start, this is 26 sort of...character templates, for players to take and turn into what they want.

That sounds incredibly tricky to balance.

You correctly identified the core issue: we've been working on it for years. Throughout development of Injustice 1, really, because that's when we started thinking about how to do this. So this has been in development for a long time. You can expect a sort of arena system, like you'd see in something like a MOBA, that will give players a chance to use the gear but still keep everything balanced.

So balancing really involves the modes, the gear itself, and then making sure the changes players can do with gear and acquiring specials and all that are balanced. To do that, we have a dedicated little team that focuses on the tournament crowd. Because we love them; it's part of our studio culture at this point. And it's really hard, it's our great challenge.

Wait, how did studying MOBA design influence this game's development?

I think MOBAs, RPGs, this is a game where we've looked at all the genres we love to play and tried to integrate the elements in a way that makes sense for a fighting game, for the first time.

How do you adapt those elements to a fighting game?

So, itemization. It became something that....we had to hire experts, and it's really a core piece of the game and a whole new skillset.

Let's circle back to the tournament crowd for a minute. What is it, do you think, that defines a tournament-grade fighting game?

I think it has to be easy to learn and take a lifetime to master. I know that's kind of a platitude, but for the most part it's...can I get in there, can I learn my specials, can I beat up on somebody, if I I'm new to the genre. And then as I go, can I learn some of the enhanced moves, things like footsies, and other advanced elements of the game that probably mean nothing to most people.

One of our goals is to get people to learn and understand that throughout their play experience, so that they can do those sorts of things. Because there are a ton of people that play our games that don't know it's there, and we spend years designing all these intricate details that are so fun once you get them. But we have to start teaching people that they're there. We have to give people progression.

How do you ease players into the deeper intricacies of your fighting game, as a developer?

So...it's time. Time is the variable we've never had before. We've tried training modes, as many have; we've tried many different things, as many other developers have. But we tend to be asking people to go into a separate mode, that's typically a short experience, to learn to play, and then we say "okay now here's the actual game."

So with Injustice 2 we'ev taken that time variable away and we're designing it so that people can play characters for weeks, through all sorts of different single-player and multiplayer experiences, and you'll progress. You'll be able to try out different things. You'll be able to spend the time that other genres give you to train, finally, in the fighting genre. Without the time, it's a very hard problem to bring players up speed on a decade of evolution in the fighting game genre.

Fair enough. What's one key piece of advice you'd give to fellow developers looking to build a great fighting game?

My generic answer is risk. One of the things that developers tend to do, as time passes, is assume things are the ways they need to be and never go back and rethink them. A good example of that is like, holding back to block in the first Injustice. It was unthinkable for us at the time; it seemed so weird for us!

Yeah, if you're coming from Mortal Kombat you're supposed to have a block button.

Right! And so that was a decision where we said okay we've done this forever, let's change it up. And that worked out, so on Injustice 2 we were like okay, anyone who makes assumptions on this team, you have to go take a time out and come back. Because everything is up for debate. So we started talking about things like back to block, that came up again, but also things like the new tech roll, how and why we wanted characters to evolve. Every single thing in a fighting game, we went back and said...do we have to have blocking? Do we have to have running? What do we have to have? And then we rebuilt from there.

That sounds like it could turn into a self-destructive loop at some point. Like, you have to eventually ask yourself what you're even making.

Yeah. Well, it is Injustice, to begin with. So we wanted to have similar gameplay: transitions, super moves, all those core elements. Because those are the things people loved, when we went back and looked at it.

But to be a fighting game, competitively, really what you need are: the basic attacks, two people one on one, with semi-equal health bars. And we did experiments from there. And at the end of the day we still loved how Injustice played, but we wanted to incorporate an entire new overarching system that kind of tweaks and pokes and changes all that basic stuff.

So if there really were no sacred cows during development, you must have been trying to distill the core elements of a fighting game. Why add in a whole new overarching system of gear?

The item system is essentially choice. In a fighting game, people always ask "what's the roster?" It's a valid question, but in this particular instance it's way more than that. There's the roster, but it's more than that: it's your roster. Batman could play a million different ways -- with some balance built into the overall equation -- so if you love Batman, you could just play Batman a million different ways, forever. Characters have completely different gear, different styles, different classes.

Seems like a handful of god-tier builds would bubble to the top. How do you keep players from clustering around a small number of optimal builds?

We have a balance team for that. We're also going to have a live team in place, and their job is to sit there throughout the lifespan of the game and do nothing but work with pro players, listen to the community, and make adjustments on the fly.

So we've actually increased the frequency with which we can update, even from what we could do with Mortal Kombat X, so we can make changes to these thousands and thousands of pieces of gear, the special abilities, and so forth.

We're at a point now where microtransactions and post-launch DLC are an expected part of big-budget game design. How do you balance a gear-based fighting game, knowing you might add additional paid gear options down the road?

The idea is the game is going to have thousands, tens of thousands, of pieces of gear on disc at launch. The thing we've always done is try and get as much content as humanly possible, up until the last second we have to submit. So at this point, we're not even thinking about that sort of microtransaction DLC stuff. There's going to be enough content. There's stuff to level up, change your character, customize your build, for weeks and weeks and weeks.