Malthusian
Talk to all NPCs in the Waldgang.

• Supposedly just rescue and talk to everyone.
  
• There are a few NPC's that randomly appear.
  
• I haven't actually gotten this myself even though it seems like I've talked to everyone I could.

Gotta Go Fast
Beat the game in 60 minutes or less in-game time. (Intermediate difficulty or higher).

• Skill and luck required.
  
• The timer only starts from a completely new game; moving to NG+ or restarting from Hardcore mode deaths doesn't reset the timer.
  
• Can be done in Training mode if that makes a difference.
  
• I don't actually know what counts as "in-game time". I recorded a video that goes on for a whole 70 minutes and I apparently still got the achievement, with only a few dozen seconds of that time spent in the menus.
  
  

Achilles
Beat the game in Hardcore mode without health upgrades. (Intermediate difficulty or higher).

• Exploit NPC buffs.
  
• Just don't actually buy this upgrade. You can still pick up and unlock others.

White Man Has Been Here
Beat the game without upgrades in Hardcore mode.

• You can do this one on "Beginner" difficulty if you really want.
  
• Exploit NPC buffs.
  
• You can still pick up and unlock the upgrades from the levels, just don't actually buy any.

Above Human
Beat the game in Nightmare mode without dying.

• Deaths during the first playthrough before entering Nightmare mode count, so don't die there either.
  
• You can safely quit to the main menu at any time during any level when you're low on health and the achievement will still count. Of course, whatever level you were just doing will reset.
  
• I don't know if the VHS Tape item will keep you safe.

Extra info in case you don't know about Nightmare mode:
Nightmare mode is only accessible after beating Hardcore mode, as it acts as the game's true New Game +. Any subsequent playthroughs within the current Hardcore mode save file are all in Nightmare mode until you start a new game from the main menu.

Banned In Germany
Have over 1000 negative social credit score.

• Beat the game, grind the last level. Maybe unlock some upgrades to help you grind it faster.
  
• If you're in Hardcore mode, get to the last level, beat the first phase of the boss, quit to the menu, go back to the last level, repeat.

Ready For Anything
Have all Black Market upgrades at max level.

• Try to get the 1000 negative social credit score achievement first.
  
• Beat the game, grind the last level.

The Gold Standard
Have 3000 Coins.
You'll most likely get this on your own when grinding for other achievements.

Keep Your Rifle By Your Side
Have 5 weapons simultaneously.
Max out the weapon slot upgrade, then acquire 5 weapons.

Storm Of Steel
Have full armour shards.
Max out the armor limit upgrade, then either find armor, buy armor from the shops, or talk to the Waldgang NPC for an immediate full armour.











Touch Grass
Unlock all Black Market upgrades and NPCs in the Waldgang.
Simply explore and grab all the red banner things and NPC's you find throughout the levels.

Reconquista
Have 8 Companions follow you at the same time.

• Do the first level, find & acquire companions, beat the level, repeat. Or just be good enough to never lose anyone normally.
  
• Having armor negates damage done to them.
  
• You can quit to the main menu and come back to reset progress from when you started the current level in case you lose one.

Relic Hunter
Own all items.

• Try to get the 1000 negative social credit score achievement first.
  
• Have loads of negative social credit, talk to the NPC in Waldgang you can buy a random item from for -30 social credits, enter any level, quit to the main menu to reset the NPC's thing, continue back to the game, talk to the NPC again for another item, repeat.

It's A German Thing, You Wouldn't Understand.
Talk to the blue otter.
I think he pops in and out between completed levels, so you might get unlucky and never see him. He always spawns in a specific spot as shown in the image here.










Mostly Peaceful Protests
Destroy all destructible objects in the first level.

• Will unlock as soon as the very last object is destroyed.
  
• Some objects can be sneakily tucked away, like in really high areas, so watch out for those.

I'd recommend doing the grind-y achievements that can be done in Training Mode first before the challenge ones for an easier time.

Cyborgs Don't Feel Pain. I Do.
Defeat a boss with only 1 health left during the whole fight.
Just don't be bad. Easiest done on the first level.

Groovy
Defeat a boss using only a Shotgun or Boomstick.

• First level. I don't know if the shotguns you can purchase count.
  
• Switch to whatever shotgun you have before entering the boss room and never switch it out until you get the achievement.
  
• Item damage, dashing, and companion abilities are fine.

Humility Is A Virtue
Beat a level using only the default Blaster.

• Find the upgrade and buy the Blaster upgrade once or twice for an easier time.
  
• Do the first level.
  
• Switch to the blaster immediately upon starting the level and never switch it out until you get the achievement.
  
• Item damage, dashing, and companion abilities are fine.

End Him Rightly
Beat any level using only melee weapons.

• Get all item melee buffs and get the NPC melee buff if you really need it.
  
• Easiest done on the first level.
  
• Immediately switch to your melee weapon upon choosing a level and never switch it out until you get the achievement.
  
• Item damage, dashing, and companion abilities are fine.

His Knightmare
Defeat the final boss using only melee weapons.

• This achievement applies to the very first phase where you have to shoot the 3 pods.
  
• Before entering The Spider's room, switch to your melee weapon and never switch it out until you get the achievement.
  
• Get all item melee buffs and get the NPC melee buff for an easier time.
  
• Item damage, dashing, and companion abilities are fine.

Handsome And Dashing
Destroy 5 enemies within 5 seconds using only your upgraded dash (Crown of Caesar).

• You'll need to acquire the Crown of Caesar item again in case you think that the tutorial one is still with you.
  
• Upgrade so you get the double or even triple dash for an easier time.
  
• The mall level, "Consoom Europe", and "The Cyberverse" have plenty of small enemies that come in huge numbers. "Cyberverse" especially has a specific enemy that multiples itself.

Incel
Beat the game without saving any unlockable NPCs.
Start a new game and just don't talk to them when you find them in the actual levels.

Burgers?
You finished the game playing as the Cyber-Flurk.
Just clear the game while using him. I did it on Hardcore Expert, but it can probably be done on any kind of game mode. You could also probably just switch to him only for the very last level in Training Mode to get this achievement.

Amogus
You found the Amogus.

• You can buy the Amogus.
  
• It can probably be found anywhere as a regular item. I've gotten it in both the 5th and 6th level from the market.
  
• You can quit out of the game until it appears in the current level's market probably.
  
• Whether or not you need Cyber-Flurk or some other requirement, I'm not sure.