This guide is designed for getting this achievement only. I recommend that this achievement and the one for Leon hardcore are your last two achievements. If they are, you will have the infinite handgun and infinite knife. You will also have a deep understanding of the game mechanics and map layout, and you will need it.
You need to know where zombies are, what windows they will break through, licker spawns, item locations, boss fight points, etc. I used a combination of guides from gamewith.net, VG247.com, IGN.com, and this website. I recommend you use one of those, or notes you make yourself from another playthrough. I'm only providing tips.
First of all, this mode uses ribbons so you need to break the game down into sections and save smart. Sections are
3.Return to RPD
4.MrX to Sewers
This is a basic example of how to break the game up. Most of the guides I used did this.
*This guide assumes you play scenario A. It’s possible on B but I found A less stressful.
You have (approximately) 27 ribbons. Try to play as though you only have 20. That allows 3 saves per section, 4 if you struggle in a particular area. This allows you to have at least 6 (hopefully more) remaining by Nest and that will allow you to save before AND after the most aggravating parts of the game. I saved 20 times and had 7 ribbons left. I am pretty sure that I found them all.
Now I will list tips somewhat randomly. Hope they help you.
1. Go ahead and accept that most sections will take a second attempt. This will make it less frustrating to reload a save.
2. If you take damage from a zombie, RELOAD. I know this seems frustrating, but I found enough supplies to fully heal around 15 times. You want to save these for bosses, lickers, Mr X, or accidental damage taken at the end of a stressful run. If you haven't went far or gotten much done, reload and try again.
3. Going off tip 2, last resort weapons can help. Have the infinite knife equipped when you know you can get it back, another knife equipped when you can't (plants, Mr X), NEVER use grenades on zombies.
4. Save your grenades for the sewers. The G monsters were almost impossible for me to sneak past on hardcore, and to kill them takes a lot of grenade launcher ammo. I used grenades as last resort on the G buttholes and flame rounds.
5. Save flash grenades for lickers. Makes them easier to kill. You need to kill them all in my opinion. Use flame or acid round, then pistol to finish off. You can exploit sometimes by standing at the doorway of a room, shooting with pistol, then letting door close, & repeating. They cannot follow you through doors!
6. Get all hip pouches! There is one less in hardcore mode than on standard.
7. Ignore the VHS tapes and all of the film with the exception of the hidden location film. It reveals location of spark shot ammo & SMG extended clip.
8. Get both spare keys from the portable safes and clear out the safety deposit room.
9. Use the stars badge to get SMG, but the silencer is your call. I personally only used it on B scenario to not alert Mr X. On A it seemed like waste of space.
10. Try to clear every room. The room will turn blue when you have everything. Pick up pistol ammo then discard it.
11. Use your infinite ammo pistol to kill ALL zombies. This allows you to explore without being harassed, and worry less when being chased by Mr X.
12. Shoot zombies that are on the ground! Most of them reanimate. Beware that there are about 5 in the game that will not reanimate until you do a certain action (puzzle or pick up item).
13. Shoot zombies in the knee to make them fall, then the head to kill them. They take more bullets on hardcore so make sure you have room to move backwards while shooting.
14. If you have to heal, use first aid sprays in the early part of the game. Always combine R+B+G and save them for the later boss fights and sewers since they also reduce damage.
15. I know I'm repeating myself but if you get hit outside of boss fights, reload instead of heal if possible.
16. Take your time! Time doesn't affect this achievement and only matters if trying for infinite smg, rocket or minigun, which if you are then you're insane.
17. Try to use only the pistol on zombies. There are 3 or 4 that require an acid round or SMG but that's it.
18. Ignore all pistols except for the SLS60 and it's upgrades. Use the heavy rounds like a magnum for the 2nd Birkin fight.
19. The first Birkin fight is possible to beat without taking damage if you are patient. Run until he starts swinging, get in a couple shots, then run away.
20. On the second Birkin I used 9 SLS60 heavy rounds, the pistol, 5 acid rounds and the crane twice. It didn’t seem to matter how much I damaged him before the crane, I HAD to use it twice to kill him.
21. On the third Birkin fight I used the SMG and pistol for his outer eyes, then the SMG for his stomach eyes. Final phase I ran and used pistol & flame & acid rounds . If you heal more than 4 times reload.
22. Fourth Birkin fight was the toughest for me. I ran out of ammo a few times before I figured out the perfect strategy. I had 5 spark shot rounds, 18 acid, 5 flame, mini gun and 4 R+G+B. You must use minigun in bursts or you will waste ammo. Make sure every bullet hits eyeballs! Alternate flame/acid rounds in between bursts of minigun. Use train to dodge when he jumps from walls, off top of train, or charges at you.
23. Save spark shot for Nest to use on plants. With Leon I recommend burning til black, but with Claire I recommend using full charge of spark shot and running past.
24. Best to save high grade powder for large gunpowder to get the most acid rounds . Also I noticed the game has 50/50 chance of giving 5or6 rounds when combining. Best to wait to combine until AFTER saving, that way you can make sure you get extra round.
25.To give you an idea of items-
*Beginning of Nest
9ribbons. 3 acid. 311 SMG. 6 flame. 1 FA spray. 7 R+G+B. 2 G+R. 5flash grenades. 1 frag. 14 spark shot
Hope this helps you get the achievement! I was dreading this playthrough but once I got going I had more fun than I did on standard. Also Claire is a bit easier than Leon due to her extra firepower, so I recommend beating his A playthrough before Claire’s.