Back 4 Blood

There are some differences between Veteran and Nightmare Difficulty to note:
1) Corruption card base challenges are harder to complete.
2) You only get 1 extra life (bots have 2)
3) You heal less trauma, and obtain less ammo in each safe room.
4) Sleepers will call a horde if they successfully grab a player.
5) Ridden and mutations have more health and deal more damage.
6) Fewer items spawn around the map.

This Act is by far the hardest, containing multiple back to back tough levels with only 1 checkpoint for the whole Act on Nightmare. The hardest level out of all of them is the level T-5 which is what we should prepare for the most.

Before you start I recommend having a few cards in your deck:

• 1-3 Scavenger/Copper cards such as Utility Scavenger, Copper Scavenger and Money Grubbers. (For Team upgrades, card shrines & to find random utility items which are usually expensive in the shop).
• Medical Professional (To give you or the bots an extra life if you/they get incapacitated).
• Well Rested (The bots all have this in their decks, having it in yours will give the team 80% overheal which converts the % portion of health which wouldnt usually heal more than your full health cap and give you it as temporary health instead, Its useful for general healing, and builds which recover temporary health.)
• Utility Belt (For extra razorwire carrying capacity for T-5)
• Build the rest of your deck how you wish but remember that the last 3 levels of this act are basically a boss rush.

With the above info and below tips you will hopefully complete nightmare and obtain the following Trophy:

• Act 3 Cleaner  

Some tips for some levels:
Farther Afield.
Using the Toolkit isnt nessasary on the harvester but it if it used, try to stay near the harvester as it crosses the field as ridden will be drawn to it. Mutations will still target the player but if they are in front of it, they should be killed by the harvester.

Blazing Trails.
As soon as you enter the large open nature trail area, a Horde timer will appear. The Charred Ridden Corruption card will also appear if not already in effect. When approaching the car park area after passing under a bridge near the end of the level, the timer will dissapear again.

Cabins by the Lake.
At the beginning of the level, there is a lake to cross. You need cross using the motorised barge otherwise it will be tough to do so. Using the Toolkit makes it move a bit faster. Regardless with how you cross the lake, a horde will attack and will be infinite until you reach a cabin on the opposite side of the lake. Be on the lookout for stingers and retches as these will target the player whilst ridden target the barge. If the barge takes enough damage, it will break and you will have to cross the rest of the lake by foot.

At the end of the level, you need to find and place a battery in a gate. Doing so will cause a special reeker horde which will spawn many reeker type enemies very frequently. I actually find it easier to purposely startle birds or shoot an alarmed door after placing the battery in as the horde caused by that temporarily overides the reeker horde timer and the ridden can be easily dealt with by using a pipebomb. Dodging reekers and retches is alot more awkward especially when climbing the hill to get to the end safe room.

T-5.
This level is by far the hardest one. Even though you only need to find and retrieve 6 boxes of research on offine mode, it is still a tough level. Hopefully by this point you would have upgraded your quick items at least once. From the shop buy some pipebombs and razor wire, I would also suggest buying some surplus amounts of both and ferrying them to the mansion.

When Dr. Rogers opens the door, have a quick look in the left or right rooms of the ground floor and grab some research. The ground and basement levels are pretty tough to retrieve the supplies from so getting a box now will help a lot. Take this upstairs and then go back down to start placing razorwire before too many ridden get inside.
Place razorwire on the staircase, position them around the corners for max effectiveness. Place any spare razorwire in the hallway upstairs. The point where we want to holdout is at the end of the upstairs hallway at the intersectiom between the front facing room, bedroom and hallway junction. The majority of ridden should die by the razorwire on the stairs leaving stragglers to appear from the hallway leading to the rear of the house and mutations which will eventually get up the stairs. Mostly tallboy enemies will cause a problem. Move the research you palced upstairs onto the outside roof terrace area.

Every so often go onto the roof terrace accessible from the corner room next to you and try to take out the ogre. The bots should help take out anything that exits onto the roof to get you.

After the ogre has been defeated, defend that section of hallway for some time until eventually the research locations appear on the hud. At this point, you should get the research boxes from the top floor first and place them onto the roof terrace, then the basement ones by heading down the rear staircase. After dropping each research box defend for a small while in the hallway area where you defended earlier. This should give the bots time to heal you or give you ammo if needed. After you have got all of the research boxes on the roof try to drop them off the edge into the front courtyard. When you have moved 5 down grab the 6th and jump into the rear of the truck and place the box on the area required. Use a pipebomb if any and quickly place the other research boxes onto the truck. The bots should give adequate coverage for you to do this without a pipebomb. Depending on the mutations that appear on the map, you may have a harder time doing this. Retches, stingers and bruisers can make things more difficult if they spawn near by. The bonus of being Holly in this act means that any ridden that die by the razorwire will give you health, and the overheal effect from the well rested cards should keep you topped up on temporary health aswell.

A Friend in Need.
Inside the funeral home, there is an alarmed door which cannot be disarmed. Opening this door will start an horde which doesnt stop until you turn off both of the furnaces. This requires you to find a keycard which usually spawns on a slouched corpse, but can also appear inside the morgue body storage units. 

Making the Grade.
Inside the gymnasium, there is a generator which needs to be started to move the bleachers. After a horde which can be defended at the toolkit room a few rooms before easily the generator will break down. At this point you need to find a battery in one of the side rooms to repair the generator, doing so will call another horde and an ogre. However, this horde is infinite until the ogre is defeated, so do not run back to the toolkit room. Use the side rooms for cover and try to take out the ogre or wait until the bleachers are fully extended to exit onto the roof. If you defeat the ogre you can progress through the level normally. If you decide to escape, you may need to use a pipebomb to safely get to the end of the level before the horde and ogre catch up to you.

The Road to Hell.
Make sure you buy some pipebombs for the end section. When you get to the middle of the level you drop into an area and the game will add a random mutation horde corruption card on a timer. This dissapears when you find the 3 chemicals and exit through the gate. The chemical positions are different each time but one is always in the first dark tent area, another in the side tented section inbetween the mobile buildings and starting Tented area and inside one of the 3 mobile buildings.

At the final area, after passing through the first gate you will want to use a pipebomb when approaching the corner leading to the second gate. After passing through the second gate, if you have any more pipebombs, use one to safely reach the third gate. You should be able to get to the saferoom with little problem from here.

The Body Dump.
On this level buy as many pipebombs as you can hold. Also get some healing items and stun guns.

When you drop down into the body dump area, an ogre will spawn. Approach a T-5 Container and open it and use one of the T-5 Grenades on the ogre. This will lower its defenses allowing you to easily kill it. Remember to pick up your pipebombs again afterwards. At this point you need to find and destroy each main nest. There are 3 and to destory them you need to destory 3 nodes connected to them. It's best to run through this area as fast as you can and throwing a pipebomb if you start to get swarmed. Another ogre will spawn as you are doing this, but you should just ignore it for now. After destroying all 3 nests you should find another T-5 container and use the T-5 grenades on the ogre to finish it off and finish the level.

Remember that T-5 grenades work on other mutations too, and will insta-kill ridden with no consequence to yourself. If you run out of pipebombs, load up on these grenades from a container and throw one at your feet if you get swarmed.