Their main purpose on Mars and Mercury is to secure Vex tech, and Golden Age human tech. That's the entire reason they move into Freehold. They also look to gain the tech to eliminate Ghosts by capturing Hive leadership on the Dreadnaught. It is unknown why they search for these technologies, but the speculation is that they are retreating from the Hive.
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The cabal empire running from the hive. Oryx would of come any way.
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Some say they want this technology to kill us and stop us from being reanimated by our ghost
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That is one of their goals now, but they have been searching long before we arrived, a time when they would have had minimal guardian contact. There must be another reason.
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Yeah maybe just a lust for power, since they don't have relation with the darkness they may try to get its mower since they encountered it
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They're on Mercury?
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They sent a patrol, as seen on the Vertigo crucible map. The Grimoire card for it is quite interesting.
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Fancy meeting you here. Don't worry, your secret is safe with me.
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Why thank you good sir. Let's keep it that way.