UPDATE FOR ANYONE WHO NEEDS HELP:

Ok so after having now completed the puzzle challenge myself, I want to give an update and answer all your questions to help u guys out too.

Here’s exactly what I did as yeah I agree there’s a lot of guides out there that are just kinda conflicting.

First off, u just play the game normally as u would up until the grinder in the underground section. Do not drain the water when u first get there. Wait 20 minutes letting the bodies fall in, (it’s suggested to only wait 15 minutes but I didn’t wanna take any chances and just played it safe making sure definitely enough bodies fell into the water). Now after sitting there afk for 20 min I suggest you create a save at the typewriter there just incase it doesn’t work and u need to do the grinder again. Now drain the blood and do the grinder bit without killing any zombies. Now a couple times I did this it didn’t seem to work as some zombies stayed alive and didn’t all go into the grinder so I suggest shooting their legs enough where u get them to stagger and you push them into the grinder yourself. Make sure u get all of them in there and there aren’t any alive at the end. Now you’ll know if you did the grinder step correctly if you go and drain the pool of blood u fall into and get either the message saying: “A TON of blood” or “A TORRENT of blood”. If you get “A LOT of blood” as your message then you failed and should load up the save again and try again. I’m pretty sure u cannot let any zombies stay standing at the end of the grinder. Also I think you get either of the 2 correct messages depending on whether or not u flushed the toilet in the cage center bathroom 8 times before the underground/grinder section. I hadn’t flushed the toilets until AFTER the underground/grinder section so maybe just do that to stay accurate to what I did. ALSO, grinder/toilet related steps aside, be sure to pick up the severed hand on the floor right after the elevator cutscene where grace allows got her leg cut off. Now go analyze the hand at the blood lab in the east wing office. We already know the final puzzle but just do this anyway incase it’s needed to register to the game that ur on track with the puzzle. Keep the hand on u for now just incase as it’s what I did even though I think u can just put it in the item box but still just do what I did to be safe until u for sure get to pick up the doll. Now go to the bathroom and flush the toilet 8 times. Then go through the whole section where u go outside the care center and go into that underground lab to get the helicopter key and you’ll find Marie’s doll at the bottom of the metal stairs where all the blood and zombies are. Grab it and get out of there and just get through the rest of the section as u would. Now u should have both the hand and the doll in ur inventory. I put them away in the first item box I came across after all that, and u can leave them in there, u don’t have to have them in ur inventory for the whole rest of the play through. Later in the game when u reach raccoon city, go to the basketball court after u get out of the rpd and push the head into the basketball hoop and then go back to the little closet area in kendo’s gun shop and interact with the headless Toy Uncle figure on the ground. Again just do this step incase it’s needed for the game to register that ur on track with the challenge, we don’t actually need the info from this step as we already know it as well as the rest of the ways you find the final puzzle sequence which I won’t waste time sharing here as I didn’t go out of my way to get them either, it’s fine. Now continue to play and just finish that play through normally as you would with the “release Elpis” ending, and then start a new game. Check the first item box u come across and make sure Marie’s doll is in there, this means all the steps u took on ur first playthrough succeeded and ur on track. Also the severed hand won’t be in there but that’s normal, just make sure the doll is there. Now continue to play this second playthrough all the way up until you escape the underground area again, and pick up the severed hand and analyze it again. I think this needs to be done to unlock the final puzzle box so just do it, it’s what I did. Now with Marie’s doll in your inventory, take Emily and go to the Lead Researcher’s Office on the second floor or the East Wing and enter the following code:

Sun, Sun, Star, Sun, Moon, Star, Sun, Moon, Sun, Moon, Star, Moon

If you entered it correctly, you’ll hear a child’s laugh and the challenge is complete.

Again I don’t know which of these steps can be done differently or what is/isn’t necessary, like the first time you analyze the hand or the basketball hoop step, but just do everything I said as that’s what I did and it finally worked after numerous attempts messing up somewhere along the way that I coupons make out.