Does this image cause you fear and terror? 

Yes? Well, I got the guide for you. Today is "how do I kill Gustav and not flounder and die horribly" day.

So, Gustav is broken up into three train cars that each have their own mechanics and range for support. Typically, we want to go from the top most train down to the bottom, as going from the bottom up will add in the support of the other Gustav train cars to the fight. Which is....not ideal. If you can pull that fight off, you really don't need this guide. 

Anyway, the easiest way to handle all of the Gustav train cars is via an SG/MG echelon. You also want a Taunt Fairy for it, as it's pretty important for one of the fights to go smoothly. This is also a fight where your machine guns will be going through multiple magazines, so using Negev/Lewis is a good idea for them. However, the formation differs between fights. So, let's start looking at each fight.

Carina

The first train car I believe is named Carina. For this fight, we want a more standard MG/SG formation. Something a bit like this:

Now the fight itself is fairly simple. Carina will do normal attacks a bunch of times, and then fire off a volley that will pick the front-most target. Since we should be using a Taunt Fairy and its skill here, it should target the fairy's decoy target. However, this means the front two columns will get deleted. So, retreat your HG and SG here so they don't die a terrible death. All of the attacks Carina does are grenade effects, so they hit multiple times on things with dummy links. This is why we use a taunt to handle this. You're sort of on a timer; your echelon needs to kill Carina before your Taunt decoy dies, but it should be doable.

Vela

The next train car is Vela. The formation you want to use for this one looks like this:

The reason for this is because the back two columns will get DELETED, so we want to move two of our MGs up to the first column. This is probably the most difficult of the three fights, as the bottom turret is essentially Judge on steroids. The good news is, it only hits one target. The bad news is, that target is going to fucking die. So the idea is that you want to retarget your MGs so they hit the bottom turret. Once the back two columns get targeted by the main gun, retreat your backline. 

The top turret fires a line of missiles on two rows. If you're using SAT8, this should be fairly irrelevant, but it can be...an issue without shielding. SAT8 is highly recommended for this, and if you don't have her, well, I hope you have P22 or HS2000 instead. Don't have any? Then it's time to go to Normal difficulty and true core mask SAT8!

Once the bottom turret dies, it's kind of just a "shoot it until it dies" scenario, though. If you're using P22 or HS2k and no SAT8, you want to only use one MG for this and have your HG as one of the dolls you keep on the front row.

Little footnote here, you may want to have some armour tile buffs on your tanking SG so the burn from Vela isn't quite as bad on EX. You do have enough time to move an MG from 7 or 1 and get to the front column, so you can maintain some tile buffs for the SG. 

Puppis

The final train car. This is a fusion of the two cars prior, so you can keep the formation you used from Vela. Which is this, if you don't want to look at the picture above.

For this one, the front most target is shot repeatedly, while the back two columns get deleted. So we want to use Taunt Fairy once again here. Move your two MGs up to 9 and 3 and just...let the shootbang happen. If anything, you may want to retarget your MGs to the turrets that come with it, but it's not that big of an issue. This is probably one of the easiest ones to kill.

So hopefully now you don't have PTSD nightmares about Gustav. God knows I will...