Here are the things I picked up while fighting this guy:

1. Try to run away from his curving bullets. Usually running into them results in two hits: the initial hit and then continuing to run through which results in taking damage from the sparkly trail they leave behind. If you take a hit from his bullet turn and run in the opposite direction because taking two hits in rapid succesion like that builds up damage VERY quickly. This will result in a lot of premature deaths if you aren't careful.

2. Stay in the top half of the screen. The bottom is very tricky to navigate so avoid it like the plague. Sometimes he'll travel to the bottom of the screen and stay there going back and forth. Let him be and do not follow him. If you walk into the bottom of the teeth at the very top of the screen you'll be able to shoot the razor blades that spawn from the top left and top right spawners (assuming you have the double pill shot at this point) while remaining relatively safe in the top middle part of the screen. The mandible's bullets can't pass through walls so he won't be able to damage you and all you have to do is constantly shoot the spawning razor blades and dodge the shots coming in from the bottom which shouldn't be too hard. By doing this you can recover health (albeit very slowly) before the mandibles come up from the bottom of the screen and engages with you again. This could save you from being defeated on his next shot if you recover enough health.

3. Keep a distance from the mandibles and when he shoots at you always go up between the teeth and then move around them (to the left or right. The shots only curve once and then they fly into the wall). Ingain that motion into your head because his shots curve and by doing this you will 100% dodge them. Just watch out for stray shots from the razor blades. You can also sometimes cheese the shots by running into the white teeth. There's a bit of space between each one so in a pinch you can run out of the way of the bullets into the teeth and they'll whiz past you. Just make sure that the sparkly trail disappears before you run out again or you'll end up taking a hit anyway. This is kinda unsafe however because the mandibles could walk into you dealing tons of damage or you could take a shot from the razor blades while standing still. For the most part run to a different part of the top half of the screen (up and around).

4. Keep the pressure on. By shooting the boss you recover health MUCH faster than you would running around. Every shot puts a bit of health back into your HP meter. This definitely saved me when I took too many hits a couple of times. Your main way of attacking should be to shoot him for a couple of seconds and then turn around, run around a tooth, circle BACk around and repeat. He only shoots every couple of seconds (he shoots increasingly faster as his health goes down so if he's almost dead he's gonna be firing pretty fast. Take this into account and adjust accordingly) so if you keep doing this he won't be able to hit you. Just make sure the razor blades don't shoot you while you're doing this. His shots travel fast so when you turn around really book it!

5. Be conservative with your flasks. ONLY shoot them when you know they'll hit the boss. There's no point in using them to destroy the razor blades since they respawn so quickly (unless there are a ton in one spot in which case definitely take them out with a flask if it's faster/ easier). The flasks do a ton of damage to the boss so you don't want to waste them. Pro tip: Remember earlier when I wrote that he sometimes goes to the bottom of the screen and stays there for while? He is usually the perfect distance away from you to nail him with a flask. If he does this lay the damage on and chuck those bad boys right at him (safely though, don't choke your win away over flasks).

6. Try to keep an eye on Remedy. The collision on the white teeth is really wierd. I've found myself trying to run past them and instead running straight into them by accident. This ususally resulted in a defeat. Try to make sure you are between the teeth before taking off or you'll end up taking stray fire from the razor blades or worse the mandibles will walk into you which is pretty much the end.

7. Don't worry about the razor blades too much. If they are near you definately take them out but don't go out of your way. They shoot in random directions and not at the same time so if you're lucky they'll just straight up miss you. If you're doing the "wait at the top of the screen while the mandibles parties uselessly on the bottom to recover health" strategy that I mentioned above then you can usually go after the razor blades easily without much fear of being shot. Their shots are too difficult to dodge though so don't put your neck out to destroy them. Only the ones in your immediate vicinity if you're clear and have time to do it.

8. Lastly don't stay in the same place for too long. You may want to camp in a corner of the screen and wait for the boss to come to you but this is a pretty bad idea not just for this game but for any bullet hell game. Always be moving even if that movement consists of simply running left and right (but not too close together. Think of it like pacing, take a couple steps and then turn around again. There's a bit of a delay from when you press a directional movement and when Remedy moves so if you're spamming the left and right buttons and razor blade shoots at you you're probably gonna get hit.) By doing this you can usually dodge the shots from the razor blades. Run around them if they come close and continue moving. Just be aware of where the enemies and are where their shots are/where their shots are gonna be. By doing this you can keep yourself safe and your health high.

So I wrote WAY more than I thought I was going to on a single boss fight haha. I honestly consider this fight to be one of the hardest in the game (took me about an hour and a half of straight attempts to beat this guy. Probably more.) and I couldn't really find a comprehensive strategy guide on it when I was struggling through this fight so I guess I kinda made one. Remember that these are just TIPS and STRATEGIES and not a definitive way to fight this boss so if one way works for you definitely go for it. If this helped you at all let me know! I absolutely love this game and helping people so it would be pretty cool if this actually benefitted someone. With that though I think I'm gonna get back to my DEATH chest run. Cheers!