Tonight, I just beat Skeletron Prime for the first time. I figured that he'd be harder than he actually was, though. I beat him on my first try. I think The Twins are a harder boss fight, as I don't always win. I had to beat The Twins a few times since I got the Souls of Fright and had Souls of Might saved up but had all 3 helmet sets and no remaining Souls of Sight, since I'd made the Fairy Bell and Hallowed Repeater with the souls from my only 2 victories (out of over 10 tries). In short, I now have the Hallowed set, excluding the Hamdrax and the Gungnir. I have a few fights left ahead of me yet.