Oh also: the yuuzhan vong traveled to the Star Wars Galaxy from another Galaxy with JUST BIOTECHNOLOGY so what I'm saying is: Star Wars is also capable of traveling between galaxy's not just halo and their precursors.
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The flood have been in multiple universes. The forerunners have access to interdimensional technology. And they were nothing compared to precursors. The precursors were not only eons ahead, but they were massive in size. Like, ginormous.