In Path of Exile: Legion, we introduced five new jewels that can alter the keystones on your Passive Skill Tree in powerful and interesting ways. One of our game designers, Hrishi, spent a lot of time developing these jewels and has shared his thoughts about this process with us in a three part news series. We hope you enjoy this first entry! We'll share entry two next week.

Hrishi's Introduction

I love keystones. They might be among my favourite things in Path of Exile. To me, they represent one of the strongest aspects of Path of Exile's build diversity. Being stunned by the possibilities they offered is one of my earliest memories of this game as a player, long before I started working with Grinding Gear Games. I can still remember loading up the wiki while my game was downloading back in beta, navigating to the Chaos Inoculation page and saying "Wait, it does what?". I was instantly sold on this game after checking out a few others such as Blood Magic which also blew my mind with possibilities.

While this write-up isn't so much about the Legion Jewels themselves, I'll have to give a little background to them, in order to understand how the legion keystones came to be.

Crazy Jewels

The idea for the Legion Jewels goes all the way back to the development of the Incursion, when I was originally coming up with concepts for unique items for the league. I was talking to Mark, one of our senior gameplay programmers, about random ideas for what we could do, and I asked if it was possible to change a notable into something else within a unique jewel's radius. "Should be possible.", he said, which sounded great, except this meant I'd need to come up with a 'corrupted' version of every single notable on the tree, and forever keep this up to date whenever we added notables to the tree. Well, that's not ideal at all.

Then, Mark had the idea of storing a seed number on the jewel itself and having that determine what the passive skills within a jewel radius corrupt into. This would mean we'd only need to create a list of possible outcomes to choose from, and would naturally work whenever we updated the tree. Still, this means it would be a fair bit of work but this is a lot more manageable and doesn't have the overhead of needing to update this every single time we update the tree.

Ultimately, we decided not to go with this idea and stick with more traditional unique items for Incursion, but the idea was there, waiting to be used one day.


It's almost a year after Incursion, and we've just finished our launch of Synthesis, which means it was time for me to start thinking of concepts and ideas for the upcoming league's unique items. Since it was immediately after Synthesis' launch, we didn't quite know what the next league's theme was going to be yet, which complicates unique design a fair bit!

After some discussion, it emerged that the league's theme was potentially going to be Vaal-themed. That certainly helped speed up the unique design process. While pitching random ideas, I remember this old jewel idea we had for Incursion and wondered if we could make it work this time around. So I started working out the details on what this would mean.

From a design perspective, the act of corrupting small passive skills and notables into something else entirely was somewhat straightforward. It just meant I had to make a set of 'corrupted passive skills' to pick from, using existing stats in the game that are themed around the Vaal. Keystones, however, were difficult. What happened if a keystone was in range of this jewel? Well, the obvious answer is it corrupts them. But what does that mean, exactly?

Corrupting Keystones

So in order to figure out if these jewels were even going to work, I had to plan what happens to keystones when they became 'corrupted'. Simple enough, I told myself, you get the corrupted version of the existing keystone! Except, it's not simple at all.

I talked to a few others and started listing out possible corrupted versions of all keystones on the tree. Yes, every single one, so everything from Vaal Acrobatics to Vaal Zealot's Oath was in this document.

It didn't take long after a design meeting for us to realise that there was no way we were going to have the resources or time to develop 20+ compelling and balanced keystones while they were tied to the ones on the tree. Also, what happens if we change one on the tree, does the corrupted version also change? What about keystones that we just want to change in the future? So many questions and it was getting way too complicated for a single unique item that we had to make the call that we couldn't really do this.

Not the end of the world though, we simply took the same logic we used for small passive skills and notables, and reasoned that we only really needed to develop a few keystones and have them replace the existing ones based on the seed number specified by the jewel. This seemed a lot more reasonable, so I set out to make five really compelling keystones that were heavily Vaal-themed.

However, we eventually realised the league wasn't going to be Vaal-focused at all. Sure, the Vaal were there, but the focus was more on the five different legions that you were going to encounter.

Okay, don't panic, Hrishi, this can still work. We simply need to make keystones for every legion, and figure out a way to make 5 variants of the jewel such that they worked differently for each legion. Of course, we'd need a small list of keystones per legion so there was enough variance, so maybe three per legion? This meant we needed to come up with 15 keystones.

... Uh oh.
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Grinding Gear Games
So many jewels
So many combinations

Perfect for min max'ing

One of the best features easily in this league
High warlord of the SUPER CUTE WALRUS CLAN
- Retired for Harvest /seal flap
I hope brutal restraint wont remain insanely rare.
IGN: Jerle_Farmer
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looks awesome
I can tell this guy is a genius
Great write up, loved it!
Notables and small nodes they corrupt are way better than the keystones. #lesshyped
Slow down for a minute to enjoy the beauty around us.
is Natalia Mark Rosewater?

This reads _exactly_ like something he'd post.
Very cool

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