This guy is probably the toughest "boss" in the game. With all forms of damage turning into a measly 1 (2 with crits), fat damage, namely melee, won't do much to help you kill one, not to mention that going melee almost ensures your death from the close range. I'm going to assume that you've beaten Moon Lord ,because without post-Moon Lord gear, this fight is extremely hard. Mounts are a requirement for this fight.
Weapons and Ammo(choose one):
- Chain Gun>S.D.M.G>Megashark>Pirhana Gun
- Chlorophyte≈Crystal>Endless Musket Pouch
- Luminite>Endless Quiver
Armor: Vortex for crits and movement speed; this can be substituted with Shroomite but id not as effective due to the loss of the buff when moving.
- Destroyer Emblem
- Eye of the Golem
- Putrid Scent
- Any set of Wings (preferrable, but not required)
- Tabi/Master Ninja Gear (to get to mountable space/asphalt very quickly, not needed if mount is ready)
- Mounts that fly or are VERY fast (e.x., Cosmic Car Key. Blessed Apple)
These accessories are mostly for the crits, since mobility is covered by the armor and mount.
A skybridge should suffice if you have already obtained either the Cosmic Car Key or Blessed Apple, but if you haven't, then a skybridge of asphalt will also work. I haven't tested the asphalt skybridge out, but it certainly seems like a perfectly viable option. You also want to have a quick way out of the dungeon, so mine out the entire area and place a platform right at 0 feet for a quick escape to the skybridge.
Kite like a man and keep him on the very left or right of your screen. The preparations are harder than the fight, and if you use all of the methods I give, you can easily finish it off!