Cross Necklace + cobalt shield + band of regeneration + regeneration potion + 60 defense + melee weapon + stand in place = easy mode destroyer fight
I recommend a flail for most of the fight, switch to a sword to kill the probes if your health is "low," they drop hearts (my health never fell below 300). Though you could probably use any kind of weapon if you really want (as long as you can kill it before morning). You can also do without the cobalt shield but you'll have to grapple the ground to stay in place. The other two accessories can be pretty much anything. A star cloak would do a little extra damage, and maybe use an emblem for your weapon of choice. You may need to use an ironskin potion to get your defense to 60 depending on your armor and the mods on your accessories.
The biggest source of damage is from the lasers, but if you're constantly being hit by the body, they won't touch you.
Make a small little box somewhere in the sky, a little lower than a sky island. Inside that box, make a little hole on the bottom most right part of it so you can shoot out of it. Stand on that hole and shoot through it. The Destroyer should never fly high enough to touch you, so while you're constantly shooting it, all you have to worry about are those flying things that can pass through walls, although usually, you'll be able to just kill them with bullets before they get to you.
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