One major change to Terraria in 1.4 is that the Daedalus Stormbow and Holy Arrows have been majorly nerfed, and that’s significant since they used to be overpowered against the Destroyer.
Since they don’t work as well as they used to, we need to add a step to the old strategy. All this requires is farming one new item, and you'll be set to annihilate The Destroyer.
Gear
The main item you should use to beat the Destroyer is actually the Black Spot pirate ship mount. This mount is insanely fast and allows infinite flight, and you can use this mount to easily beat all of the mechanical bosses.
The wiki says that the Black Spot has a 25% drop chance, but I got super unlucky and literally killed the Flying Dutchman 20 times before it dropped. However many times it takes you to get it, it’s an amazing mount worth farming.
With the hardest part out of the way, you should use either Titanium or Adamantite armor with the ranged helmet. I was stupid and didn’t realize I had the melee one equipped, so I made it harder on myself.
But, it turns out that the melee helmet is still very effective. If you're having trouble beating him, try using the melee helmet for higher defense.
For your weapon you’re going to want the Daedalus Stormbow reforged to Unreal if possible, along with at least 1,000 Holy Arrows.
For accessories you should use a Magic Quiver or Molten Quiver, along with a Ranger Emblem. Since you’re using the infinite flight mount, you don’t actually need movement accessories, so you can use more damage boosting items if you want.
Arena
Now that you have all of the items, should should make a pretty small bridge with regeneration items. I used the same bridge I fought Queen Slime with, and the main purpose of the bridge in this fight is to collect the hearts that fall.
The bridge is also completely optional, but I found it made a difference for me. It also helps to be far off the ground since the Destroyer is such a long boss.
The Destroyer Strategy
So before I started the fight, I used an Ironskin Potion, an Archery Potion, and a Shrimp Po' Boy that increases health regen. After spawning him, fly straight into the air and start shooting the Stormbow at the Destroyer. The two main things to watch out for are the probes and the lasers he fires, but both can be outrun with the flying mount.
If you get overwhelmed with probes, fly away from them and take them out before continuing. The probes constantly drop hearts, so you can go down and collect some if you’re low on health.
Overall it’s really easy using the mount, and you just have to keep firing at him until he dies.