Neon Abyss

As the description says, you need to beat Hal, the God of Machines, without taking any damage at all. Hal is the boss of the sixth floor. 

This is obviously challenging, but what you can do to make it as easy as possible is to not only play on Easy difficulty, but first kill yourself over and over on Easy difficulty such that there is only one dot above the Easy poster in the bar. The more dots above the difficulty, the harder it is. Die over and over to lower the dots to just one. This is now the easiest possible difficulty. 

The run itself leading up to Hal is unfortunately at the mercy of RNG. Ideally, you'll get an item that lets you fly (Divinity or Pegasus), as it makes the second phase of the Hal fight a piece of cake. However, the most important thing to focus on during the run leading up to Hal is gun level and gun damage, as well as bullets and fire rate, if they're applicable (they aren't applicable if you're using a laser weapon). Basically, ignore anything defensive on your run and only take stuff that improves your damage. If you can find a Soul Bringer weapon, you're pretty set. 

On each floor, I highly recommend using the Save Reload Exploit if you mess up the challenge room and don't get a gun upgrade. Beating a challenge room without getting hit guarantees a gun upgrade, so use the exploit to ensure you get it on each floor. This will allow you to go into the Hal fight with a very strong gun regardless of what weapon you have, making the fight far shorter. 

As for the fight itself, the first phase is the toughest because, depending on your weapon, it can be hard to see the projectiles raining down if your weapon is taking up a lot of the screen. I therefore recommend standing off to one side while you shoot him in the first phase, because if you're right under him shooting straight up, you're likely to miss a projectile falling down amongst your bullets. 

For the second phase, if you can fly up, you're golden. Go directly above the blue ball, right in the center, and his blue balls he shoots out will never hit you. The lasers rarely use a pattern that'll reach you in the air, but if they do, you'll have to improvise. If you can't fly, you should continue to stand off to one side while you shoot the core, paying attention only to the lasers so you can avoid them. A homing weapon is great here because you can focus entirely on dodging and don't have to worry about aiming. 

If you get hit, use the Save Reload Exploit to start the floor over again. Unless you get some significantly helpful on the sixth floor, just beeline right to the boss fight to try again. Also, don't worry if you get hit right at the end. Even with the boss dead, you can still use the exploit to start the floor over as long as you don't enter the portal.