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) Less items spawn around the map.

This act does not really have anything Nightmare specific except for on the Handyman level. This act is probably the second easiest after Act 4. Nontheless there are still some pretty tough parts.

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.)
• Hyper Focused for extra weakspot damage. (You will be fighting several ogres, and breakers throughout this campaign)
• 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 2 Cleaner 

Some tips for some levels:

A Call to Arms.
On this level you can get a Toolkit room in the parking garage. If this appears here, you are able to skip the nest/node section of the level completely.

The Handyman.
One of the hardest levels of this Act. Try and have several fall back point for the constant hordes you will be facing. 
The final big node you destroy will always have Bob's Arm; therefore it is best to leave the one in the police station until last since the door to use the Arm on the end the level is here too. In Nightmare, this level adds Monstrous Mutation corruption cards secretly for every giant node you destroy. For this reason, you should destroy all of the little nodes around the map first and then destroy the big ones in quick succession to end the level without too many monstrous mutations spawning.

Pipe Cleaners.
On this level, I recommend having 2 pipebombs. The first for the horde which appears near the beginning when you open the door to the sewers. This door closes, and if you don't proceed through before it closes, you have to try again. A pipebomb will help you get through before the door closes.

At the end of the level, you will need to open another door with a control console. This horde is infinite until the end of the level though. You should defend in the upper area where the console is until you see the door is open enough for you to proceed through. When this is the case, use the pipebomb and climb to the end of the level.

Trailer Trashed.
After untethering the boat and crossing the broken bridge, you will enter the trailer park. When you approach, the area a timer will appear on the top left. This is for a mutation horde card which gets added to the corruption cards list without notice. These can be stinger / tallboy or reeker hordes so be prepared.

The Broken Bird.
After attaching the first crate, I prefer to defend from the toolkit room on the boat until the helicopter returns for the second crate which should be marked on your hud by this point. After attaching the second crate, a breaker will spawn, however this break will not call a swarm circle, nor is it required to be defeated to finish the level. Either use pipebombs and keep evading until the final crate can be attached or defend from the Toolkit room again until ready.

Heralds of the Worm Part 1.
This is the hardest level in my opinoin followed closely by Part 2. On this level, you will an absurdly high amount of mutations spawning when the ogre spawns until it dies. For this reason, you should take out the ogre as fast as possible. There will be a minigun set up outside of the gate, and a toolkit crate to the left with another portable minigun. You should get this minigun and position it at the gate and use this to kill the ogre fast. After the ogre is dead, an onslaught corruption card gets added. This is more managable and you should only have to deal with around 1 or 2 hordes before reaching the end of the level.

Heralds of the Worm Part 2.
On this level, you need to defeat an ogre and a breaker. The ogre will spawn as you approach the open gate on the otherside of the building in the middle, and the breaker will spawn when the ogre gets to half health.

The problem with this is that you could find yourself fighting both aswell as a horde if the ogre isnt killed fast enough.
When you leave the safe room, there's a truck which may have a minigun on the top. If it is not here, it will be in the adjacent corner down the road on that truck instead. You should defend one of these two corners depending on where the minigun is. Take some time to buy extra supplies if required to help take them down by dropping them off the railing from the safe room and ferry them to whichever corner you are defending.

Grave Danger
This level is a simple 3 step process.

Make base at the central church by placing as much razorwire outside the front entrance as you can.

Kill each snitch one by one and defend against the resulting hordes inbetween inside the church.

Kill the last snitch and get to the church as fast as possible so that you can fight the breakers here and the swarm circle doesnt force you out of the church. There are 2 breakers to fight though so bring some explosives and maybe a pipebomb to lure the horde away if they start to become troublesome.