My biggest and most important piece of advice for getting this achievement is to switch to keyboard and mouse. Most of the game plays better with a controller, but in this case, I found it a lot easier to manoeuvre around Tor Namun’s attacks with my keyboard, especially during the third stage. I tried several attempts to get this achievement with my controller but when I switched to keyboard I beat it on my first try, hence my recommendation.

Secondly, I recommend against beating this boss on NG+. From my experience, I found the stages a lot faster to beat when using a file of my first playthrough than with NG+, especially the second stage.

Lastly, if the achievement doesn’t unlock at the end of the fight, don't panic. Just wait until the end of the credits and it will pop up. Don't restart the level until you KNOW you've been hit. If you think you're in the clear, let the credits roll and it will tell you if you got the achievement or not.

Now, onto the stages.

For the first stage, keep an eye on Tor Namun. When she turns red, that means she’s about to hurl rocks at you, so stay alert. They shouldn’t be too hard to dodge, there’s a big enough space between them to weave through. If you want to be extra safe, you can jump down to the inner pillar where you can avoid some of the attacks. At the final stretch of the stage, there will be four consecutive rock attacks that you need to look out for and dodge. Once you do that, you'll be in the clear until the next stage.

This is where the fight gets tricky, but the most important thing is: DO NOT JUMP. Just keep sliding left and right to avoid the laser attack and collect the orbs. Keep pressing the action button so you can launch your attacks as fast and frequently as possible to keep the stage short. At one point, Tor Namun will launch a wall of fire attack at you, in which case, slide to one side and stay up in the air for as long as possible until the attack passes.

Now, if you're using a file of your first playthrough and have been religiously attacking Tor Namun, you should be able to avoid most or even all of the third attack, the falling orbs of fire. If you still end up at this phase, keep an eye on the telegraphed attacks. You can manoeuvre around the attacks at the bottom, but not the ones up the ramp; stay down, wait for the attack to cease, and then go back to gathering the orbs.

This part should be easier in comparison. As you collect orbs, Tor Namun will use her laser attack again. This time, use your keyboard to press the left (a) OR right (f) button and hold it until the attack ends. Do not jump, don’t switch buttons, and don’t slow down. Once you're safe, continue gathering orbs. After you land enough hits, the Dolphin will arrive. Simply follow the quick time events to attack Tor Namun, and then rapidly press the action button.

When that’s over, Tor will add fire traps around the pipe. If there’s a full ring of fire, jump over it (double jump or charge jump). If it’s a partial wall, simply slide around it (don’t jump). Keep landing hits until the Shark arrives, do the quick time events, and smash that action button, and then you’re done!

Honestly this achievement isn’t too hard, it’s mostly just tedious that you can’t skip the cutscenes. From what I understand the devs either can’t or won’t make the cutscenes skippable, but I hope they can at least add checkpoints between each stage so that you don’t have to start ALL the way at the beginning if you do get hit. But for now, I hope this helps. I added a video guide from PowerPyx (I am not affiliated with them, but they do great work for achievement hunters) at the end of this section for anyone who needs a visual aid. Let me know if you have any other tips/tricks or recommendations to get this achievement as quickly as possible.

Thanks for reading, and happy hunting!