Nobody Saves the World

As the description says, you'll need to earn all 36 medals (i.e. get a gold medal on all 12 trials) and then head up to the top and talk to the Dueling Faces (and then turn in the completed challenge, like for all DLC achievements).
 
Like with the base game (and especially the NG+ dungeons), this DLC is all about putting together the proper build to deal with each trial. Only a few have important execution, but many are easy once you know what build to use. Below, I have laid out each trial with the exact build I used and then some details on my strategy or approach. Unless I state otherwise, each build was extremely reliable in terms of success rate and ease of use. However, that being said, if you find yourself struggling with my approach, don't hesitate to try out a different Form or different passives. I will say that I stand by each of these though, in terms of how effective they were.
 
Note: Despite "Power Defense" being the "first" trial (i.e. the one on the left of the first room), don't do it until you've completed at least two others in the first room, unlocked the Mechanic Form, and then leveled up that Form to unlock the Rattler Turret. The Turret is an absolute necessity for "Power Defense." I mention it again in that trial.
 
Also, in almost every case, every passive I used below was at level IV. I had already fully upgraded all of the best ones from the base game, and I went into this DLC having over 100 upgrade tokens left over. However, I have made explicit note of where I felt having a passive at level IV was a necessity, and anywhere I haven't noted it, I wouldn't suggest spending tons of tokens without first attempting the trial a few times to see if you can simply manage with them at their current level.
 
Break the Crystals
 

• Rat Form
• Magic Life (level IV) passive
• Gallop (level IV) attack

No other passives or attacks matter, since this is just a speedrun. Gallop at level IV is a necessity to move fast enough, and Magic Life at level IV is necessity to ensure you don't run out of health before reaching the end. Avoid the green slime splattered on the ground right in the beginning, as that's the only thing on the entire course that can slow you down (you don't need to worry about touching the purple ground throughout the course). Use Gallop nonstop the whole time, never letting go. Magic Life will pull your health so you don't have to stop using it. You'll need to learn the course a bit to get 25 seconds for gold, but it's a very short course and not much that can go wrong. For the narrow opening, go past it, up, then rightward into the side of it, then straight up. That's a guaranteed way to get up every time without having to aim or anything. For the whack-a-mole crystals, just do tight circles in the area until they all are gone. This shouldn't take more than a few attempts to get it down.
 
Dark Arena
 

• Magician Form
• Zomnomnom passive
• Blood Pact passive
• Crit King passive
• Hat Trick attack

No other attacks are really needed. Spam Hat Trick (spawn Familiars) and just stay in the light. Let your Familiars do all the work. If you end up near enemies, feel free to hit them with to build up more mana for more Familiars, but they should have no problem taking care of all of the enemies. Avoid the bomb enemies at the end of the first wave at all costs. They will destroy your health. Purposely run as far from them as possible so the explosions don't touch you. The second and third waves should be easy with your Familiars doing all the work.
 
Swift Strike
 

• Ghost Form
• Poison Tipped passive
• Mermaid's Resolve passive
• Zomnomnom passive
• Hat Trick attack

The goal here is hits, not damage. My strategy was to spawn as many Familiars as possible since they can all hit over and over, meanwhile continuously have the attack from the Ghost going, which hits over and over. On top of that, the poison damage you inflict also generates hits every time it does poison damage. Start the fight by spamming all your Familiars to spawn as many as possible so they're already there as soon as the boss spawns, then spawn more as soon as you have enough mana. Stay in close and move around the boss to avoid the smash attacks. Move away when he's about to spin attack, then back in. The spin attack will likely kill all your Familiars, but I always had plenty of mana to spawn more from all the damage your regular attack will be doing. I was able to get around 315 hits first try with this method.
 
Power Defense
 

• Ghost Form
• Zomnomnom
• Blood Pact
• Quick Cooldown
• Arrow Flurry
• Water Spray
• Rattler Turret

For the "first" trial, this is a very long and stressful one. The passives and attacks are pretty critical here, because you can only hit the enemies a certain way. I have no idea how gold would be possible without the Turret, so before attempting this one you should do the above three, and getting gold on two (six medals total) will unlock the Mechanic. Leave the Colosseum and head back to the main map so you can level up the Mechanic Form (refer to Job's done! (25G) for that) at least until you unlock Rattler Turret. Now you're set for this trial.
 
Place turrets nonstop. Unfortunately, each time you pull the lever to start a new wave, all your existing turrets are destroyed, so immediately start by spawning one and always spawn another as soon as the cooldown is done. The more turrets you have, the easier this will be. The first stage (three waves for bronze) are pretty easy because enemies don't have wards. So, just stay in the upper left corner of the inside of the track with your Ghost attack always on, and you'll do a ton of damage as enemies round those two first corners. The silver and gold stages have enemies with wards, and so you'll want to stay near the spawn point, continually hitting enemies with the appropriate attack (arrows or water for Sharp or Light, respectively, since your attack takes care of Dark and your turrets take care of Blunt) to get rid of their wards, that way your turrets can do all of the heavy damage to finish them all easily. The last wave of gold can get pretty hectic with all four wards, but you should have many turrets by then, your regular attack running continuously at full strength, and just shooting arrows or water as needed. The final enemy has a ridiculous amount of health, so you'll easily want 10+ turrets spawned for it, and you'll still likely need to follow it around most of the track with your Ghost attack to finish it off in time.
 
Hard Shelled Enemies
 

• Ghost
• Quick Cooldown
• Blood Pact
• Zomnomnom
• Fireball
• Rattler Turret

This is one of the harder ones, and took me around three or four attempts because the timing is really tight. Regular enemies need to be hit 10 times to kill them no matter how strong the attacks are, so you need quantity of hits over strength here. Your regular attack as the Ghost will take care of that, along with the turrets you place. Elite enemies (ones with the yellow crown next to their health) only take damage if the attack does at least 30% damage. That's where the Fireball comes in, as this attack does massive damage. So start by using your attack (and keep it active the whole time by pressing again whenever it turns orange) and a turret, and continually drop a new turret every time the cooldown is done. As soon as you see an elite enemy spawn, immediately spam it with Fireball over and over, killing each one. The enemies and their spawns are exactly the same every time, so it's going to be a matter of getting used to the spawns and knowing when to quickly start spamming Fireballs. If you stay diligent about placing turrets, you should have a ton by the end to help out with both types of enemies.
 
Whack-A-Melee
 

• Ghost
• Zomnomnom
• Blood Pact
• Mermaid's Resolve
• Hat Trick
• Rattler Turret

Every enemy dies pretty quickly, so this is about how many enemies you can kill as fast as possible. To do this, flood the area with Familiars, and use Turrets every so often as well. I set a turret right at the start, and spawned a new one every so often to help out. Meanwhile, mash Hat Trick to send out Familiars constantly. Do circles around the arena while maintaining your standard attack throughout. The bronze and silver stages are very easy, so you won't even need turrets. Just spam Familiars nonstop. For the gold stage, I needed to use turrets. Only then did I fly past the target.
 
Status Pileup
 

• Ghost (Fear)
• Poison Tipped (Poison)
• Stun Powder (Stun)
• Zombite (Infected)
• Fire Ball (Burn)
• Blob Lob (Slow)

This one is very easy and should take only a few seconds. Press to use your normal attack and then just cycle through your other three attacks, one after another, two or three times, and this trial will be done in seconds. I did something like --------- and the trial completed with a gold medal, first try.
 
Dark Speedrun
 

• Rat
• Gallop (level IV)
• Ethereal

Do NOT equip Magic Life. If you take any damage, you fail the trial, and losing health from Magic Life counts as damage, so eliminate the risk by just not equipping it. Similar to the earlier crystal trial, you're going to be charging around at full speed with Gallop. However, the critical thing for success in this trial is realizing that the spinning flame obstacles also count as light to keep you going. You will need to use Ethereal to pass through them, using them as shortcuts and avoiding taking damage thanks to Ethereal. The route is a little awkward to describe in text, but the course is so short that it should be easy to follow. I broke it down as follows:
 

1. Head directly up through the flame spinner with Ethereal. Release Ethereal as soon as you pass through, and walk to the edge of the next obstacles.
2. Gallop diagonally up-right through the first moving light circle and then switch to Ethereal to pass through the flame spinner as you head up into the light path.
3. Immediately go into Gallop to sprint around the corners of temporary light and up to the top, stopping at the edge of the light to await the next light circles to appear.
4. As soon as the light appears, Gallop straight across all the way right (you should have plenty of time to go straight across without stopping, as long as Gallop is at level IV) and continue around the corner into the temporary light. Making sure you get into it before it "moves down" is important.
5. Walk down with the appearing lights, not using Gallop at all, and only trigger Ethereal if a projectile is headed directly at you, ending the course at the bottom.

One of the most important things here is conserving mana so you don't run out. The easiest place to conserve it is at the end, because you're at the mercy of waiting for the appearing lights anyway, giving you plenty of time and room to dodge projectiles yourself. So don't bother Galloping, and only use Ethereal when necessary. You'll likely need to take the first few attempts slow to learn the course and patterns, but each attempt is very short. This trial will likely take you more attempts than any other, but you'll gradually get the timing and directions down.
 
Dance Dance Defender
 

• Ghost
• Quick Cooldown
• Barrier Coil (level IV) 
• Rattler Turret
• Arrow Flurry

This one requires the most skill with execution. Here is how I made it as manageable as possible. Map Barrier Coil to and Arrow Flurry to so their use is intuitive with where the wards comes from (Light wards come from the left, aligning with , and Sharp wards come from the right, aligning with ). Rattler Turret will be on and unfortunately the opposite of its source (Blunt wards come from the bottom), but this is unavoidable. The goal here is, much like DDR games, to hit the "notes" right as they enter the center of the arena. You can "cheat" by using placed area attacks to do continuous damage for you, hence when I recommend Ghost (with its continuous Dark attack from the attack) and Barrier Coil (a continuous Light attack). Barrier Coil is unlocked via leveling up the Mechanic, which you hopefully did during the first trial room like I recommended above. Quick Cooldown is necessary to ensure you never are stuck not being able to use either of those two area attacks. For the Blunt wards at the bottom, keep a Rattler Turret down there. Make sure to place it as far down and center as possible so it always prioritizes those enemies. If you keep your aura attack around you for Dark wards at the top, and drop Barrier Coils on the left for Light wards continually, and maintain a turret at the bottom, then you can just focus on shooting arrows to the right. 
 
Barrel Breaker
 

• Ghost
• Mana Shield
• Quick Cooldown (level IV) 
• Horsepower (level IV) 
• Ethereal
• Pump Up (for quick mana consumption) 

This trial only ends when you die, so there is no time limit. The goal here is to recover mana as much as possible while avoiding dying. However, as the trial states, you can only recover mana if you've actually used some. So you'll need to balance using mana with recovering it. Here was my strategy, which I used to far surpass the requirement (and felt like I could go on forever if I wanted).

First, I want to note that there is one way you'll be recovering mana in this trial: by breaking barrels with your attack (of which Horsepower adds to how much mana you get per barrel). However, know that there are two ways you'll be consuming mana: using attacks such as Ethereal and Pump Up, but also taking damage from the rocks. Mana Shield means when you get hit by a rock it'll drain mana instead of just health, and it'll drain a substantial amount of mana. However, you need to balance the mana drain from rocks with the health loss from rocks, to ensure you don't accidentally die. Here is the pattern I used:
 

1. As soon as the trial starts, using Pump Up until your mana is entirely drained, then immediately use your attack.
2. Sweep through the rows of barrels, allowing your aura to destroy them all, which should build up mana relatively quickly. Once you know the placement of the barrels (they are the same every time), you will likely be able to clear out most with still enough time to move out of the way before the rock comes.
3. Once your mana starts to fill up, let a rock or two hit you to immediately take of a significant amount of your mana, giving you room to recover more.
4. As your health gets low, use Ethereal briefly each time a rock is coming to let it pass through you without damaging you
5. Repeat with letting a rock or two hit you as your mana fills up, and cycle through these steps over and over until you get a gold medal. Remember, the trial won't end until you let yourself die.

 
Ward Swap Boss
For this trial, you need to fight the same boss three times, once for each medal, with tighter requirements each time. I used a different build for bronze and silver, but it didn't work for gold, so I'm just listing my gold build since it will make short work of bronze and silver.
 

• Form doesn't matter (but a fast one such as Horse, Killer Bee, etc., is best)
• Crit Cleric
• Slug's Secret
• Poison Tipped
• Pump Up
• Killer Sting

The goal here is to kill the boss as fast as possible, so this fight is all about DPS. What you're going to do is break the boss's ward, then spam Killer Sting over and over as fast as you can until the ward regenerates, then break it again and repeat. Killer Sting always crits, and once the boss is poisoned it'll be doing double crit damage thanks to Slug's Secret. Killer Sting is also Sharp damage, so it'll take care of that ward for you. Pump Up takes care of the Blunt ward but also gives you Attack Up too, so two for the price of one. Get in close to the boss and just mash Killer Sting over and over, only stopping to use Pump Up when it puts up a Blunt ward, and you should be able to tear through the boss's health.
 
Way of the Passive Fist
 

• Ghost (not important) 
• Steel Plated passive
• Smite passive
• Strongman passive
• Pump Up

Thankfully a very easy one to end on. This one is more like a puzzle than a test of skill. It's all about equipping the right passives. Here is how to break each dummy without hitting them.
 

1. Dummy 1: Pull a lever, let the bomb come toward the dummy, and once it's about halfway there, let it get close enough to you to stop and dash. Get out of the way and let it blow up the dummy
2. Dummy 2: Equip Steel Plated. Pull one lever and stand right next to the dummy. When you get hit by an enemy it will cause Sharp damage to the dummy
3. Dummy 3: Equip Smite. Use either the remaining enemies from the previous dummy or pull the second lever in the previous room. Take damage near the dummy but remember that Smite causes lighting to strike the enemy, not you, so try to get the enemies next to the dummy while they attack you rather than you standing between them and the dummy, causing the lighting to miss the dummy. If your Smite isn't upgraded at all, you might need to take a ton of hits from the enemies to finally get lighting to proc, so make use of the health all around this dummy so you don't die while waiting for a lightning bolt to strike.
4. Dummy 4: Equip Strongman. Pull a lever, lure the enemies over in front of the dummy, then go down about halfway down the room, then use Pump Up to knock the enemies up into the dummy. Pump Up isn't necessary, but I tried with Tail Swipe and it kept making me lunge up too far and counted as me hitting the dummy. Pump Up is a safer bet.