User blog comment:The terraria helper2/DESTROYER HELP/@comment-62.163.237.225-20120127181302

get a block of hellstone or meteorite. Build a small arena above the ground. Make sure you have a hook, at LEAST cobalt armor/Mythril armor, and a decent sword or mace (Dao of Power would be awesome if you have it, its easily obtainable). Accessories that are recommended would be: Philosophers Stone, Cross Necklace, Star Cloak, Band of Regeneration, feral claws or Warrior's Emblem (any of those 6 will do). However, if you can't get those, focus on anything that improves your defense. Ideally you have the following potions (2 of each or more): Ironskin, Regeneration, Thorns. Make sure you have a lot of healing potions (preferably greater healing potions) on you just in case.

What you do, is attach yourself to the meteorite/hellstone (needs to be ORE for meteorite). This should deal 1 damage with proper defense, and if you have the philosophers stone this means you are invincible longer than usual. Your regeneration will keep the damage minimised, even IF the Destroyer manages to hurt you (or his orbs). While hooked, you can constantly swing at the destroyer. Dont focus on his orbs, they'll come to you eventually, dropping hearts. If you build 2 walls around you (3 blocks high) a lot of the lasers might not hit you either.

Its a very solid strategy, though the Philosophers Stone makes a big difference. I mentioned the Star Cloak because it adds a solid amount of damage from continously being hurt by the fire. This same strategy, walls included, works miracles on the Twins as well (though higher defense becomes a MUST due to the flamethrower). Good luck! -Volt-