[spoiler]Didn't play unity yet, just know of the phantom blade and play AC2 at my friend's because she has it and we just dick around in it. Isn't the sword of Eden the thing that shoots lightning? I'll YouTube it.[/spoiler] The retracting blade would have to be transmuted to form such a potent form. In order to do that, I would have to place a storage of a certain alloy I developed (that can be compressed into smaller chunks but still retain the same amount of mass which it can be reverted to) for what the blade will come from and be made out of. Next, I would have to inscribe runes within the structure of the hilt and guard to smooth this procedure. Finally, I would just have to add some sort of trigger or activation to the grip, so you can activate it by will at any time, and the blade will form via using the stored metal as a material and an equal trade for its transmutation.