Tiny Tina's Wonderlands

This achievement requires you to complete the "Puns and Crimeishment" quest at the highest (i.e. fourth) difficulty level. Each difficulty level works the same way: most rooms have you complete simple objectives, all of which are marked on your map. As I noted in the roadmap, this DLC felt markedly more difficult than the previous two, mainly because of some annoying objectives and enemies in this one. Even so, I found that I could ignore enemies in the majority of rooms and just complete each objective and escape in the portal as soon as I was done. Each run starts with some simple platforming where you need to head over a bridge, through a hole in the wall, up some platforms to jump over a gate, and then onto a turret to destroy the drawbridge chains to open the castle door. You then need to kill the badass troll (feel free to ignore the other enemies) and head into the main chamber of the castle. This DLC is laid out a bit different from the others, as it isn't linear. Instead, there are four individual rooms you need to tackle to break all four chains in the main room. I will discuss these starting from the left and going clockwise around the room from where you entered.
 

• The first room on the left is the mine, and to access it you need to pull a switch to lower a bridge to get across. This is what you'll be doing throughout this room. Shortly after you spawn into the room, a minecart will come in and stop, and the obvious switch will become available to interact with. You now need to follow the minecart along the tracks, interacting with fourth switches along the way to lower four bridges for the cart to continue, all the while being constantly attacked by many enemies. As soon as the cart reaches the end, a portal opens right back where you started, for you to leave.
• The second room on the left requires you to go under some pistons that crush downward. Don't worry, they barely do any damage to you, so feel free to tank the damage. This room has the same pistons throughout, and they also do barely any damage. There are three switches on ground level that you need to interact with first, with tons of enemies shooting at you. Once all three are pulled, you need to get up to the top floor, then jump out onto one of the two purple launch pads to get launched to the area above the entrance. Over on the far left pillar is a skull chain you need to pull to activate the turrets. Now you can jump back down to the ground and exit via the portal.
• The third room (back right) requires you to stand on a pressure plate on the floor to make flames shoot out of the nearby grate. You need to stand on it for around 10 seconds to it to melt the huge chain above you so you can access the door to the room. This room functions the same way, and is a massive pain. You need to melt three chains in the same fashion, but enemies are swarming you nonstop, and it's really dark so it's hard to see the small goblins coming, and they do a lot of damage. It also seems that you need to stand on the switches for the full time uninterrupted to finally get the chains to melt, making this room quite frustraing and definitely the most difficult of the entire bunch. Once all three chains are melted, get into the portal as fast as possible.
• The fourth room (front right) requires you to shoot and destroy the three red crystals leading up the path to make the portal spawn. The room requires you to do the same: there are five pillars/mountains, each with three red crystals on them. Shoot off all three crystals five times to open the portal. This room is quite easy to just keep running, ignoring all enemies and just shooting all the crystals.
• With all four rooms completed, you can interact with the four switches in the main chamber, which then opens the portal to the boss chamber. This boss fight has three phases. First, you'll be in a room with a giant mechanism in the center, spinning around and shooting various things at you. Your goal is to destroy the fourth yellowish soul crystals on the underside of the top of the machine. Take note that the energy orbs being fired at you barely do any damage, but if/when those orbs with fire decide to shoot flames out, those flames do significant damage. Your shield will immediately deplete and your health will drain over halfway, just from a single touch of these flames. Avoid them at all costs by staying crouched when near them. After all four crystals are destroyed, all of the things shooting at you stop (so you're safe from the machine) and Fyodor jumps down. He shoots at you extremely slowly, so just keep strafing and he'll never hit you. Shoot him until you take off 25% of his health, and he'll go invincible and teleport you out of the arena. This is the third phase, where you in a separate gauntlet of obstacles that you need to jump down into and get to the launch pad at the end. As with the machine in the middle, if you see orbs shooting flames, avoid them at all costs. They will instantly destroy you no matter how good your gear is. The next highest priority to avoid are the bullets with legs that run down the gauntlet. If they run into you and explode, they do a large amount of damage too. The energy orbs and the pulsing things on the ground do barely any damage, so don't worry about them. Focus entirely on dodging flames shooting out, jumping constantly to avoid the bullets and everything else, and get to the launch pad as soon as possible. The launch pad sends you back into the area to repeat again with the crystals on the machine. Do this all four times to finally kill Fyodor and complete the quest.

Now here is the critical part. Completing a run theoretically unlocks the next difficulty level, but Gearbox has made the decision to only introduce one new difficulty level per week. This means you would potentially have to wait a month to have access to all four difficulty levels. There is thankfully a way around this barrier: force close the game app, go into your settings, Network settings, and choose to 'Go Offline.' Now launch the game, head back to the mirror, and you should get an option to scroll right to increase the difficulty after interacting with the mirror. Do so, and complete it on difficulty levels 2 and 3. With that done, and now that you can access and see difficulty level 4, while still in the game, open your Network settings and choose to go back online. Now simply play through and complete the run on difficulty level 4, and this achievement will unlock as soon as you kill the boss.