Guide:The Destroyer strategies

The Destroyer is one of the bosses unlocked when the game enters Hardmode. It is extremely strong, dealing very high damage to the player even when the player has high-tier armor. It is generally recommended as the first boss to fight following the Wall of Flesh.

Terrain Preparation
The type of preparation you'll be making depends on your approach. If you are using melee, The Destroyer is best fought on an arena consisting of tall walls with multiple layers of Wood Platforms. This will allow players to move around the arena freely, and to keep a good watch on where the boss is. If you are using ranged, pick a wide, open, flat area, with plenty of clear space for flying and dodging. The Destroyer can clear a lot of vertical space. Like any other burrowing enemy, it can only control its movements in tiles/blocks.

Armor
Mythril Armor or higher is highly recommended for this fight, as The Destroyer hits quite hard. Note that full Adamantite armor will reduce damage from body segments down to 17 or so, making this boss fairly easy to solo if you do plenty of mining first.

Melee
If a you have enough defense then you can go in swinging with a melee weapon, but be prepared to take some damage from the Probes that spawn from its body. Melee is quite strong in this fight, much as it was against the Eater of Worlds. Each swing can hit multiple segments at once, and since it's health is shared through all of it's segments this can lead to massive damage. A Phasesaber is a good option as its damage is high and it is fairly easy to acquire by this point. Large weapons like the Breaker Blade can make things easier by extending your reach. Spears are effective for the shear number of hits you'll get for each click.

Ranged
If you've collected a Clockwork Assault Rifle from the Wall of Flesh then it would be a good idea to use this against The Destroyer. Piercing rounds such as Meteor Shot can hit multiple segments on each shot, dramatically increasing damage output. Crystal Bullets are also a very good choice, since each of the shards that break off also deal damage (Like 10-20 per shard) to the boss, and the shards pierce. If the assault rifle is not available, then an Adamantite Repeater loaded with Unholy Arrows or Hellfire Arrows Should do fine. Ranged characters should equip some form of wings as they should probably spend most of the fight high in the air.

Hellfire Arrows will hit 4-5 parts in most cases. Holy Arrows do slightly less damage per hit, but summon 3 fast, penetrating stars, easily making up for the lack of brute power. Holy Arrows also have the added benefits of helping to control Probes/mobs that spawn during the fight and possible re-use. The true downside to Holy Arrows is acquiring them: Pixie Dust is easy enough to farm from Pixies, but you also need Unicorn Horns from Unicorns, which are a rarer spawn. On the bright side, 1 Horn = 35 arrows. (Hellfire Arrows are easy to acquire once you have 1.1 equipment to use down in the Underworld to mine for Hellstone.)

A Clockwork Assault Rifle could be viable with Crystal Bullets, though that method may take a while due to The Destroyer's fairly high defense ratings. It might pay to keep that weapons to deal with the Probes and mobs, however. [Note: I've personally attempted this with a Megashark and Crystal Bullets, as I was trying to farm Soul of Might. While viable, damage over time suffers from the Megasharks lower damage. It'll work. It just takes longer. The Clockwork Assault Rifle is comparable to the Megashark. I wound up switching back to my Repeater and Arrows.]

A Ranger Emblem helps a bit with the extra damage. Also, if possible, a Star Cloak is advisable. You will get hit often, so taking advantage of that fact by returning the favor in the form of stars helps. The Destroyer is very long, so you're bound to hit it.

Accessories should be reforged to either increase defense (if you're not good at evasion) or damage (if you're a decent dodger.) An Obsidian Shield is advised for the increased defense and no-knockback effect.

Magic
Magic users are going to have extremely low defense, and are going to have the hardest time with this fight. If you have a Demon Scythe then it is highly advised to spam it like crazy, with the help of a Mana Regeneration Potion. A Laser Rifle would also be a good choice because of it's high rate of fire, but wouldn't deal nearly as much damage as the Demon Scythe.

Potions and Buffs

 * Hunter Potion - Depending on your setup, this can be very helpful to track The Destroyer movements underground and dodge it. Also makes sighting mob spawn easier since this is a night fight.
 * Ironskin Potion - A combination of melee adamantite armor, ironskin potions, and an obsidian shield will reduce probe damage to around 20 and body damage to a paltry 10.
 * Bowl of Soup - Further stat boosts.
 * Swiftness Potion - Easier dodging.
 * Thorns Potion - Most of the damage you will be taking will be from contact with the boss.
 * Regeneration Potion - Survival boost.

Shine Potions and Night Owl Potions are helpful, but not really essential. They just make sighting other mobs and the terrain easier. Featherfall Potions and Gravitation Potions are also useful if you want more control while in the air or have limited access to the three flight accessories.

The Fight
The Destroyer is almost exactly the same as the fight with the Eater of Worlds, in that it digs around and launches up at you every chance it gets. Just sidestep the body and keep wailing away at it. Occasionally it will launch a few volleys of Death Lasers at everyone fighting him. These hit for about 15-20's on players with 40-50 defense. The Destroyer also spawns Probes throughout the fight. It spawns them very often at first, and then the spawn rate slows down a good bit as you kill them off. Probes drop a 20HP Heart when killed at a 100% drop rate, so for the most part health isn't an issue with this fight, combined with the regeneration potion, and any health potions you have.

Like most other bosses, if everyone is killed The Destroyer leaves. The Destroyer will also leave if you cannot kill it before sunrise. After a few minutes of bashing away at it's health, the machine will fall, but be warned that the loot spawns at the head when killed. Since Souls are not affected by gravity, this can make them very difficult to find after the fight has ended.

Melee
Keep swinging your sword toward the destroyer, when he starts firing lasers, start jumping around platforms. The walls of a proper arena should block most of the lasers, making the fight much easier. Try to focus on the probes since they are the primary source of damage you will be taking. He should go down in around 5 minutes.

Ranged
Fly. The trick is to stay above The Destroyer and not get trapped under it. If you do, take the hit from the body and get out from under it. It's VERY long and can easily turn back in on itself and not give you breathing room. Also, if you're using Hellfire Arrows, you run the risk of killing yourself from the AoE damage. Keep at range and above it as much as you can while letting loose fire on it. Even if you can't see it, keep firing if you at least know the general direction it's in. It's long, so "spray and pray" is actually a viable tactic. (If you hear the metallic "clinking" hit sound effect, just keep shooting in that direct until you see it again or the sound changes.)

The Probes are both a blessing and a curse. A curse as they get in your way and can attack you for decent damage with their lasers (a bit more if you collide with them). They are a blessing in disguse, however, as they can be a source of health by killing them when you have less that full health: They can drop Hearts for later healing. The same can be said of the regular mobs that spawn during the fight. Careful management of Health Potion usage and Heart collecting will keep you nice and stocked on health (along with use of the Renegeration Potion.) Just drop to the ground when it relatively clear and gather some. The Hunter Potion will let you see The Destroy in the ground, so you'll know if you have to evade instead or can keep going for the hearts.

A secondary weapon for use against the Probes and mobs can be handy, especially if using Hellfire Arrows as your main weapon. The Probes follow you, so you can easily damage yourself with Hellfires if they rush into close right before you fire on them (or get in the way when firing on The Destroyer.) It's even mopre important if you end up on the ground. Inadvertantly firing at your feet with Hellfires can easily ruin the fight for you.

If you're fighting on a wide, flat plain, it might pay to occasionally just run across it until The Destroyer appears. Doing so might cause it to spread a large portion of its body along the ground, making it an easy target from the air. If you have the horizontal space (and speed), make use of it by flying a decent distance back and forth instead of only staying in a particular (horizontal) area to help spread its body out. The more of the body you can keep exposed (and accessible to attacks), the more opportunities you have to deal damage.

On the other hand, if you want to hit the ground (say for gather Hearts), you can fly straight up and hover a while until The Destroyer jumps straight up at you. You can then drop to the ground quick to gather what you need/want while the The Destroyer recovers from its attack attempt. It takes a while for it to loop back around from a high jump. Remember, outside of solid blocks/tiles, borrowing enemies have little control of their movement. This give you the time to take a breather or collect some pick-ups on the ground.