Your first big showdown in the house is going to get a bit messy.
Resident Evil 7 Guide: Walkthrough #6 - Getting the dissection room key
So, if you're following our guide you just backtracked into other areas of the house, avoiding Jack, and picked yourself up a shotgun. Now it's time to go back downstairs. Expect more fighting and more molded monsters... but, no, we wouldn't advise you use the shotgun if you can help it. Save it and those shells for a desperate situation.
You should absolutely drop by the save room next to the stairs, but when ready head back down and into the labyrinthine basement/processing area. Near the green/blueish door you forced open earlier there's a wooden door. Head inside. Within you'll find some gunpowder and some other goodies, but the thing we're most interested in are the body lockers.
You'll see puzzle notes pointing you to find "Three As and a Handprint". Look at the names on the various doors in the room. You want to locate a locker named for somebody with Three As and one with a bloody handprint. That's Tamara - near the far end - and the handprint, closer to the door. Easy.
Doing this will open up the locker closest to the door you entered from. When you activate it a molded will pop out. Once it's dead, grab the DISSECTION ROOM KEY that was in the container with it.
Onwards to the dissection room
Once you've got the dissection room key, head out from that room and head towards the other areas downstairs (abuse that map!) that you haven't yet explored. You'll know you're going in the right direction when you pass through a room with multiple baths.
Look inside and around these baths as you pass them. You'll find stuff like shotgun shells, handgun bullets and chem packs. As you round the corner, look for a hole in the wall populated by a herb. There are enemies too, of course.
Listen: It's going to get dicey down here, and there's not much we can tell you to help. Remember our advice from earlier: plant your feet, place your shots carefully, go for the head. Avoid using the shotgun if you can, but if things get desperate, go for it. If you use the shotgun and aren't getting a kill with every shot you should stop, though. That ammo is too precious.
Eventually you'll reach a boiler room. At the back of that, there's a door. Use your newly found Dissection Room Key to go on through.
Boss preparation in the dissection room
Story break! After a very brief story sequence, there are some items to grab in the room you're in and the subsequent hallway:
- On your right there's a locker with some shotgun shells.
- Further downstairs still there's a herb right in plain sight.
- Near the herb there is also some ammo - for me, shotgun shells.
Once you've grabbed all that gear, head through the doors. Boy, this area sure looks... arena-y, doesn't it?
Head upstairs, and duck into the door on your right. This is an alternative entrance to the room you just came from. On this side you can find some chem fluid on your right as you enter. Leave and then carry on the way you were going: upstairs, you'll see the final dog head you need just hanging on a hook, obviously a trap.
If you want, before you take the bait you can head down the nearby stairs - down here there's some gunpowder and a locked door.
Okay, you can't put it off any longer - it's time to take the bait.
Boss fight: Jack and the Giant Chainsaw
Okay, so... the first phase of this fight pits you, with whatever you walked in with, against Jack. Jack has a giant chainsaw. You have to fight him with a chainsaw of your own...eventually.
There's a way to do this without actually firing a shot. See all the body bags hanging from the ceiling? If you get close to them you can kick them. If you do this to Jack enough times, he'll get frustrated and move to pick up a bigger weapon, which kicks off phase 2 of the fight. This is really hard to do, since you have to kite around the room, turning around to then kick the bags into him. It can be done, though.
Alternatively you can just shoot him. Both will work. Shooting is easier, but means less bullets for you later on. I personally would favour a mix - try to encourage Jack into positions where you can hit him with the body bags, but if he gets too close blast him with the shotgun at close range.
You'll know when he reaches the second phase - he'll take a knee and get back up without his weapon.
Beating Jack in the chainsaw fight
After taking a knee briefly and exploding in a bloody mess, Jack will get up and very calmly walk over to a grate at the side of the room and rip it open. Use this chance to heal, if you need - he's not on you at this point - then prepare yourself for another round.
Follow him over to the grate, because there's a weapon behind there for you too - a chainsaw. Yours is a lot smaller than his scissor-like setup, but take what you can get...
This boss battle now becomes about blocking with R1 and attacking with R2, giving it everything you've got to kick his ass. Blocking is absolutely key - if you don't do it at the right times, you'll die in a terrible and bloody mess, simple as that. If you end up locking chainsaws with Jack, spam on the trigger until you escape the deadlock.
There's really no specific trick here that I could tell - it's all about timing. Block when he attacks, hit him when he's open. If you're really desperate you can switch to your gun as well and just try blasting him but you've been given the chainsaw for a reason.
This is a war of attrition, but keep it up - although it doesn't feel like it, he will go down eventually.
Once he does, it's time to move on to part seven - and get out of the house! The ordeal is far from over, however... but you've earned a reprieve, at least.