It will be the third StarCraft II product and will be released separately from the other two games, Wings of Liberty and Heart of the Swarm, occurring after them chronologically, beginning immediately after the ending of Heart of the Swarm. It was expected to be priced as an expansion in 2009. However, it will now be released as an independent installment, not requiring StarCraft II vanilla to run. It will receive a simultaneous PC/Mac release. The beta is intended for release in the first half of 2015.
"You are Hierarch Artanis, leader of the mighty protoss race. Years ago, your homeworld of Aiur fell to the merciless zerg Swarm. Now, at long last, you have raised a powerful fleet of warships known as the Golden Armada, and are poised to reclaim your world. But an ancient evil—Amon—threatens this destiny and the fate of the entire galaxy. Only you can reunite the protoss factions and defeat the coming darkness before it consumes all life in the sector."
The protoss were being systematically exterminated and were dying out from sheer age even before the Great War. The protoss have been picked off one-by-one, and their shattered civilization will fracture as something even worse happens, forcing a leader to save them from annihilation. Various protoss factions will be united for a last stand against Amon.
The protoss will be at the forefront of the story. Jim Raynor and Sarah Kerrigan will feature in the story, but Amon is the primary issue. Chris Metzen has likened the story to that of the film 300, with a small force engaging a much more powerful one in a desperate last stand. The storyline will conclude the StarCraft II trilogy, but is written in such a way that those who haven't played the previous installments (a possibility as per the game's stand-alone status in terms of installation) will not be lost.
"We want to get that feeling of 'We're the Protoss and we have technology that you haven't even dreamed of. We will literally turn you into a parking lot if you mess with us.' We want to get that sense of power without the focus on a single character."
Legacy of the Void is primarily a singleplayer expansion. The campaign was intended to focus on Zeratul as its main character but the focus changed to Artanis by 2014. Zeratul will still feature prominently however.
The protoss campaign will be based on diplomacy as the protoss factions splinter. The player will work with different protoss tribes and sects, helping leaders of some sects which will anger others. Using units from one side may preclude using units from the other side and alienating one or another sect may cut the player off from part of the campaign. New allies will bring with them new technologies and techniques. This forms the basis of the game's army customization. The ultimate goal of the campaign is to unite the various tribes into a viable, unified force that can ensure the protoss' survival.
It is intended that the game's campaign have its own feel distinct from Wings of Liberty and Heart of the Swarm. In the latter, Kerrigan composed a great portion of her forces' strength by herself. For Legacy of the Void, it is intended that no single protoss warrior be comparable to her in that regard via gameplay. Zeratul may be an exception, but any such missions would be based on stealth (e.g. assassination). The power of the protoss in the game is to come from the protoss as a whole, not a single individual.
It has been indicated that Nova will make an appearance in the game, and hinted that the hybrids will play a "critical role."
Blizzard intends to focus on micromanagement (to avoid simply using large unit clumps), harassment, and constant attacks in the new expansion. "Passive time", such as the low-activity early-game, will be avoided. Changes include reducing the amount of minerals and vespene gas in order to encourage the creation of new expansions. The starting worker count will increase from 6 to 12, and the starting buildings (command center, nexus and hatchery) will create more supply, psi and control to make creating new workers possible).
Mech and air upgrades may be split for the game.
By 2013 Blizzard Entertainment had begun working on Legacy's story, scripts and missions. As of February 2014, Blizzard was "hard at work" on the game. By August 2014, the development team was in discussion concerning community suggestions pertaining to the expansion. The game was formally revealed at BlizzCon 2014.
New artists were brought onto the game's art team that had not worked on Heart of the Swarm.
The story of Legacy of the Void was the first point of development for the game, as the gameplay of StarCraft II had been solidified with the previous titles. The story was worked on collaboratively between James Waugh, Chris Metzen, Samwise Didier, Jason Huck, Allen Dilling, Justin Thavirat, Matt Morris, and Dustin Browder over the period of several months (Waugh was the lead writer). As of August 2013, the game's story has been written, many of the cinematics have been completed, and voice actors have begun work. As of November 2013, Dustin Browder was satisfied with the game's story, but felt the missions and campaign mechanics needed more work, to make them "feel" like protoss missions. It was intended for the story to have the following tenants:
Create a distinctly protoss story while wrapping up the story threads of the StarCraft II trilogy—keep the story focused on the protoss and their lore.
Create an epic end times scenario for the player to stand against—deliver on the threat of Amon.
Through the nature of the Khala, it is intended that the game explore themes of collectivism vs. individuality.
In 2011, Chris Sigaty expressed doubt that new units would be added to the game, and that if they are added, it is likely that other units will be removed from multiplayer. This was refuted by Blizzard employee Kevin Johnson in 2013 stating that "no new units isn’t a direction we’re considering or have ever considered." New units were revealed at BlizzCon 2014.
↑"The Protoss are sort of a troubled species. They're being systematically exterminated, and were being exterminated long before the Zerg arrived. They were starting to die out from their sheer age, but now that the Zerg came and their home world is gone, these guys are really having a lot of trouble." Dustin Browder, Jonathan Ross. 2009-06-29. Destructoid interview: StarCraft II's Dustin Browder. Destructoid. Accessed on 2009-07-23
↑"What we're talking about for the Protoss campaign is -- y'know, the Protoss are a shattered civilization, right. They've been beaten and pummeled by the brutality of the StarCraft universe for years and years and years now, and we might bring into the campaign something even worse happens to them, and they ultimately just fracture into all these different factions. And so you are working as one of the Protoss Heroes trying to re-unite the Protoss before annihilation." Dustin Browder et al. 2009-09-04. BlizzCon 2009 StarCraft 2 Fansite Q&A - Part 4/5. Youtube. Accessed 2009-10-07.