I Finally Beat The Final Boss The Second Time After like 10 Attempts!
.....And then I proceeded to rush over to him and trigger the exact same ending as the first time because I'm an idiot. Now I have to do it all over again to get the true ending FML.
The weirdest part is how much harder he seems the second time. I beat him my first attempt the first time through, and now this second attempt took 10 tries. I think to do it again it won't take 10 but it'll still take me a few. He's incredibly tanky and I haven't found the right gun to use yet. On my winning attempt I used the Myriad Chakram. I have 100+ hours in Returnal and haven't struggled at any point in Saros. This is for sure the hardest boss in either game...