I have had this theory for a long, long while, but I've been too lazy to put it in here. So think back to year one- before the Thorn Era, before shotguns, before all that. Think about when Vex Mythoclast was at its prime. This happened once people started beating the Vault of Glass for the first times. But the Mythoclast, surprisingly, went under the radar in terms of lore. People saw, "time space gun" and "future technology" but not much far past that. I wasn't satisfied with that. No, I knew there was more to this weapon than meets the eye, so I dove in. [u]The Grimoire[/u] The description of the Vex Mythoclast is not important, nor does it go past a funny pun, and most of the Grimoire card is expendable as well. But, it does bring up one very good point: This is a Vex weapon. Vex technology, burns, material, design, this weapon is 100% Vex. In the words of a good friend, "It looks like you ripped a Goblin's arm off and started shooting people with it." So, if it's Vex, why does it fit human hands [i]so perfectly?[/i] (read Grimiore). A good theory is that, just like the VoG armor, the material morphs to your body (Hunter boots description). But I think it goes deeper. [b]Disclaimer:[/b] The rest of this theory I totally pulled out of my asshole, but looking at the whole thing, it made sense. There is no hard evidence to support [i]any[/i] of this. [u]Vex Mythoclast Origin[/u] That doesn't mean where it was created- that means where it was found. The Vault of Glass. There are [i]so[/i] many Vex structures- why wasn't the Mythoclast found in the Citadel, the Vex's home base in our solar system? Because the Vault of Glass [b]is not bound by time.[/b] We all know that. But that's actually why the Vex Mythoclast can exist in the first place. So why does time matter? Because I believe that the Vex Mythoclast comes from an alternate dimension and an alternate time- the future. "That's not possible. We've never been to an alternate dimension." Actually, the Vault of Glass is an alternate dimension in itself. But even inside it, there are [b]two alternate dimension/time portals in Atheon's chamber.[/b] This is important, because Atheon controls the broken and fluid time inside the Vault- when he dies, the portals close, you're back on Venus, etc. He is the link between all the dimensions and times the Vex have been in or will be in- with him gone, those links break. What I'm trying to say, here, is that I think you actually find the Vex Mythoclast [i]inside one of the two portals in the Vault while fighting Atheon.[/i] The Mythoclast, and the Vex as a race are both inside these alternate dimensions because they are in a dimension where they are in a war with humanity- not Fallen, not Cabal, not everyone, just humanity and the Vex. I think it's where Pocket Infinity is from, too. I think, based on Pocket's description, Pocket Infinity is beta Vex Mythoclast- humanity's first attempt, in this alternate dimension where the two are at war, to replicate and make for humans, Vex weapons (they're both exotic Vex inspired full auto solar fusion rifles.) And I think the Vex Mythoclast is the [i]finished product[/i]- humanity's successful attempt to make a Vex weapon to fight the Vex with. I think in the other dimension, all human foot soldiers equipped Vex Mythoclasts. So why do you get the weapon [i]after[/i] Atheon is dead? [u]How the Mythoclast got from their world to ours[/u] Engrams. Freaking engrams. Think about it- what are engrams? They're not cardboard boxes with weapons inside them. No, they're pocket matter- decrypted, er, pieces of air that can be decoded to become a solid object, not unlike solids becoming liquids or vice versa. I think, once in the VoG portals, you picked up a Vex Mythoclast engram. A decrypted Vex Mythoclast, right in your Guardian's back pocket. ([b]Pocket[/b] Infinity, anyone?) And the reason it's not decoded or in your inventory as an engram is because the weapon can't quite decide which world to be in- the Vex technology inside it, and thus, the Vex mind, knows it shouldn't be in two dimensions at once- so it gets stuck as a piece of matter. Now, you carry that around for the duration of the boss fight. As I said before, Atheon is the link between all the dimensions tied to the Vex. Once you kill him, that link is broken- the Vex Mythoclast engram in pocket all of a sudden thinks that the alternate dimension never existed, and that there is only one world for it to exist in, this one, so it decodes itself and becomes the Vex Mythoclast, solid form, here and now. Pretty cool, right? Rahool ain't got shit on space robots. Another cool thing to think about is that all of the Vex across all universes are one mind- so when you shoot a Vex with the Vex Mythoclast, you're not killing the Vex, you're just assisting their suicide. Make sure to check out my other lore posts about Osiris!