One Reborn is more bark than bite. And more celestial eldritch horror than bark. The way it is born of the low, red moon is spine-tingling. A dripping, viscous mass of tortured body parts that squelches towards the Earth as it uncoils itself from its lunar shackles. This boss would make Lovecraft shudder. Fortunately, this is one of Bloodborne's easiest bosses, as long as you know what to do. You're in the know, right?
The first step to this boss fight is actually to ignore the boss entirely. Run to its left and up some stairs to get onto the upper levels of the arena. There you will find four Chime Maidens who will heal the cosmic abomination and hurl fireballs at you. Obviously, they make the fight a lot harder than it needs to be, so kill them before trying to take on the boss.
Take It On
Once you head back down to the human centipede, go to its mid-section and attack it. It has a hard time hitting you here, though you’re not invincible, so be wary. One Reborn is weak to fire and bolt, so bring some Fire Paper or Bolt Paper and apply it to your weapon of choice to get some bonus damage off. It resists arcane damage though, so don’t bother with spells.
The main way One Reborn can fight back is by striking at you with its many, many legs. When they start to flail about, back up so you don’t get trampled. These can hit surprisingly hard and can almost stun-lock you, so when it starts chittering just move away. Instead of staying in the middle, you could target its larger limbs at the front or back, as crippling these will deal big damage. Also, you can stagger this boss after doing enough damage. If you do, run to the front and attack the drooping torso there.
It also uses some magic that deals arcane damage, so try equipping any armour you’ve found that increases your arcane defense. Two of these magic attacks are very easy to dodge. If you hear the rear torso screaming, back away as it’s about to do an area of effect blast. If you see the front torso lean forward and retch, back away as it’s about to vomit all over the arena. These attacks can both be dodged as long as you’re being attentive. Another arcane attack that’s a bit more horrifying is called Rain of Flesh, where One Reborn will summon a cascade of body parts to rain down from the heavens upon you. Dodge away from the limb rain and hide under the sides of the arena.
This is definitely one of the easiest bosses in the game, but don’t get cocky, kid. Be aware of what the two torsos are doing and you should get a pretty good heads up before any seriously deadly attack.