Read that st 14 card about osiris, I believe he transformed himself into a vex mind and will have something to do with the next vex raid if it happens
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No, that's a lie. His sanctuary on Mercury known as the Lighthouse was raided, and Osiris was killed. He's obviously a SunSinger, so he pretty much self resurrected and studied the Vex, wandered their portals and worlds, until someone told him "Hey! You! Come back! I miss you!" so he came back and now we don't know where or who he is.