Dark Origin is the secret bonus mission of Brood War. In order to unlock this mission you have to finish Zerg mission 9 "The Reckoning" within 25 minutes. In Dark Origin you play with the Protoss hero Zeratul and a couple of his brethren. In the mission briefing you get notified of that fact that Zeratul is actually looking to reunite with Artanis, but on your way to Shakuras you have been interrupted by some Protoss power signatures emanating from an uncharted moon nearby. Zeratul decides to investigate the moon, for it could be Artanis and the other Protoss survivors...
However, as soon as Zeratul and his brethern land on the dark moon, they notice something strange is going on there. The Protoss sensors detect a small Terran compound near the energy signature. As Zeratul looks into this matter he finds something that is e ven more strange, the Terrans have been able to
craft a Protoss pylon to power several makeshift
stasis cells! And that's not everything yet, the computer terminals of the stasis cell tell us that each stasis cell houses a test subject. These test subjects are Protoss, Zerg and Terran units. It seems like someone or something is heavily experimentating with Protoss and Zerg units! To who the Terrans in that mission obey is still unclear...
Untill you encounter the last stasis cell. It may seem impossible but, hold on, there is a Protoss/Zerg Hybrid in it! Zeratul can't believe his eyes. Then suddenly a man with a hollow voice begins to speak to you. It's hard to reckognize, but it appears to be Samir Duran! Duran and Zeratul have an interesting conversation. Duran says he "serves a far great power, that has slept for countless ages and that is reflected in the creature within that cell" (the Hybrid). Also he says: "This creature is the completion
of a cycle. It's role in the cosmic order was preordained when the stars were young. Behold the culmination of your history!". Ofcourse, Zeratul is frightened, scared and disturbed. Left with the unsettling knowledge of the Hybrid, Zeratul returned to his ship
and left the dark moon behind. Unable to explain his numbing discovery to his companions, he could only sit and
fear for the future of the universe...
Not only does this mission make you want a sequel to StarCraft more than ever, there are also some other interesting things about this mission. Let me explain:
1. Each Stasis Cell you encounter, contains at least one unit. Normally I didn't destroy the Stasis Cell's, but this time I decided to do so. Eventually, my army was reinforced by 2 Templars and 1 Archon. There were also Zerglings included by one of the Templars and one Stasis Cell contained an Infested Terran. Needless to say, they were hostile. Unfortunately, I couldn't destroy the last Stasis Cell with the Hybrid in it. I don't think anyone can, because it's set to "invincible". Anyway, if you knew about this already, it is interesting to question yourself what the Infested Terran was doing there in the first place. Does Duran need the Terran genome as well for his Hybrids?
2. As soon as you have destroyed all three Ursadon's on the map, a Broodling appears at the corpse of the last Ursadon. First time I couldn't believe my eyes, so I decided to kill them all again, with the same result. I guess I never before destroyed all 3 Ursadons on that map. It's a strange trigger though, why would Blizzard want to do that? The Broodling has an infinite lifespan by the way, which makes it even more odd.
3. After these two interesting things, I decided to look which sounds and triggers are used in the map. Really soon, my eye fell one of the wave files entitled "Gettin' Jiggy Wit' It". No, I'm not kidding, it's supposed to be in the Bonus mission. I had never heard of it before. I uploaded it to my server for those who don't have the time to look it up or don't have MPQView (or a similiar program). Besides this wave file there are some other things Zeratul said during the Bonus mission which aren't in the game or on SCLegacy. For example Zeratul used to say: "I must be getting old." Blizzard removed it for some reason from the final version of Dark Origin. Here's the wave file:
Please note that it's very likely that this is the replacement for Fenix' quote in Zerg mission 3: "How do you Terrans say it? I can still throw down with the best of them!" (thanks to Kimera757 for that one).
Source: Dark Origin mission transcript