Why Blizzard needed to teach its AI to jump in World of Warcraft: Battle for Azeroth

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World of Warcraft isn't just relying on dungeons and raids to keep players engaged for its next expansion, Battle for Azeroth. Two new activities, dubbed Island Expeditions and Warfronts, are being added to give players some variety in their progression and endgame experience. The latter is still largely under wraps, but the former was available to PAX East 2018 attendees. I came, I saw, I got my butt handed to me, and spoke with the developers about what sets Island Expeditions apart from WoW's other activities. 

While there are plenty of new ideas and concepts being introduced via Island Expeditions (the overall concept is, after all, a race to collect an entirely new resource called Azerite), perhaps the biggest difference this time around is Blizzard's approach to enemy AI. Alongside the usual basilisks, giant spiders, and other creepy crawlies of the WoW universe, Island Expeditions will be home to more advanced NPCs representing the opposing faction.

In other words, if you're a Horde player and you start up an Island Expedition, you'll encounter NPCs fighting on behalf of the Alliance, competing against you to collect the requisite amount of Azerite before you do (and vice versa if you play as Alliance). But what makes these foes any different from the millions of cultists, demons, and other AI-controlled baddies you've mowed down in the past?

For starters, they're way more dynamic and perceptive. Rather than running straight at you and standing still while you mash your hotkeys, they move around quickly and unpredictably. They interrupt your spells and use crowd-control effects. They use their own abilities reflexively, not simply on a timer-based rotation.

They also change from island to island. One Expedition, you might be going against a highly aggressive team and want to stay grouped up for a better chance of survival; in another Expedition, you might face a more defensive-oriented group, allowing you to split up and conquer objectives in a more spread-out attack.

"These guys are far more dynamic than any NPC you've maybe seen before," said WoW lead encounter designer Morgan Day. "We wanted them to fill that role and fulfill the fantasy of fighting against and competing against this enemy faction team." While making these NPCs tougher to fight was certainly a large part of that, there was another crucial element to making them feel alive: the ability to jump.

A different kind of Turing test

Working on World of Warcraft is an iterative process, with even the smallest changes potentially creating waves that ripple through other systems. And as far as waves go, balancing the Island Expedition NPC AI had the potential to create a tsunami.

Producer Daniel Stahl pointed out that, as the team worked on them, the advanced NPCs often leaned too heavy on pure difficulty. "Advanced NPCs are meant to be challenging, but they can also be way too challenging," Stahl said. "They have their own abilities, their own desires about how to play, they have goals that they're trying to achieve, and you can certainly dial that way too far, to the point they seem too good... That uncanny valley between what feels right and what's fun - you can certainly go too far with that if you're not paying attention."

Even on the show floor at PAX, I was told that the success-to-failure ratio was roughly 20 to 80, with most players losing handily. Of course, these were pre-generated characters, some of which haven't yet had their class tweaked for the upcoming expansion, and nobody had access to their favorite add-ons, so the team expects that ratio to even out over time. Even so, it was clear early on that Blizzard needed to do something more than simple number changes to keep the advanced NPCs from feeling robotic.

Day explained how the team found the answer: "We were working with this idea of selling this enemy faction team, which has a presence on the island, and what that means. How do we sell that idea, that fantasy of 'I'm Horde, there's gonna be an Alliance faction presence here' when they're NPCs, not players? And one of the things we noticed when we were fighting against them was like, 'You know what they don't do that players do? Jump. They don't jump!'"

"So we were like, okay cool, what if these things could jump on occasion? Just whenever they felt like it, really. So we went and told our amazing gameplay engineer and he was like, 'Yeah I can do that!'"

Stahl interjected. "No, first he said, 'Our creatures don't jump, dude!'"

Day laughed. "True. And we're like, 'But what if they did?' So the next playtest, after he had taken that feedback and put it in the game, it was like, 'Now they won't stop jumping!' After that playtest, we asked for a jump slider bar." While it seems like the NPCs are in a good spot now (I didn't notice an obnoxious amount of jumping or lack thereof when I played), Day jokingly said that perhaps Night Elves should jump more often than others. Why?

"When a Night Elf does a flip you're like 'Yes!'" Good enough reason for me.

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