Ironically, I think the hardest fight I had in this game was the Destroyer in 1.1, first playthrough. FIRST, my problem was not having good enough defense, even though I had full mythril armor (hey, I said this was my first playthrough). After getting full adamantite armor, my NEXT problem was learning how to properly dodge. You know how the Destroyer is actually pretty easy as long as you avoid touching it? Yeah, I didn't really do that part so well. And then the LAST problem was actually beating the thing in a single night. Yeah. I couldn't even do enough damage to it to beat it in one night. In retrospect I was probably focusing too much on killing the probes and I might have put the arena a little too high up for the Destroyer to reach it all the time, but for a while I could survive the fight, just not win. I didn't even have the same problems with the other mech bosses, just the Destroyer. I probably fought it like...at least 10 times before I actually beat it.