I want to tell you these first as you can fail to get them during a playthrough.

Roguelike
Reach and defeat Archdemon in Roguelike mode without using any fountain

Use editing custom_settings.txt: Change fountainsEnabled from 1 to 0 to disable fountains.
Seams to work, thank you @Sv. Prolivije.
Further below see how to reload your saves in case you accidentally made a missclick.


Starving War
Defeat Archdemon[and other bosses] without purchasing Cauldron

Gives some extra challenge but the bosses are still not that hard, go casual if you want to be save.

Hell yeah!
Finish hell [and other levels] without dying
A! A! A! A! Stayin' Alive
Finish 20 games in a row without dying

Just don't die. Try again with your next character or reload a backed up save.

Choose short games if you feel unsafe.

Wikipedia[de.wikipedia.org]
Download&Tutorials[cheatengine.org]

I give you just a minimal explenation.

Open process: r2g_launcher.exe

• Money, Experiance: 4 Bytes (Great Numbers)
  
• Runes, Health, Mana: Byte (< 256)
  
• Most others, 2 Byte

In Cheat Engine enter the current value of the value you want to change. In game play until it changes. In Cheat Engine update it. Repat until your sure you have found the correct values and addresses.
Now you can manipulate it.

Runes and Money are what you need or you will have to grind a lot.

Captain Planet
Equip all 5 rings at once.

The Alchemist
Equip all different potions at once.

Eeny, meeny, miny, moe

Barrel, barrel, Zombie, barrel. Barrel, barrel, Zombie, crap!

Left Click on the things in the description in that order Barrel, barrel, Zombie, barrel. Barrel, barrel, Zombie, crap! Where crap is the +1 gold: Slightly used coin.

This is best done in the catacombs, maze or the cook level are good alternatives.

While doing this you can't collect other items. Best clear the level and keep zombies, barrels and slightly used coins arround.

---

You probably will often fail but when I got my achievment I realized that it is a bit more friendly as thought.
I clicked on barrels and zombies but had no Slightly used coin arround. Continued to kill (hold mouse) the last zombie and luckily it dropped the crap and I got the achievment.

Keep trying until you got it.



Game of Crows
In the town you will see the crows. When you click on them one will create a music note.
Now continue to click on the others, a wrong one will give a bad sound the next correct one will spawn a music note again.
Continue and remember / write down their order until you get the achievment.

Hypochonder
While it's easy I realized it takes quite a while. Everytime you finsh a level or are close to start / exit and have some health missing, go back to the town and heal yourself.
There is also the roguelike variant, spend 100.000 on heal. On massacre difficulty healing becomes even more expensive.

---

I skip the other easy and self-explanatory ones like kill 1000 gargoyles.

If you think a certain one is missing, let me know.

See also my other guide how to get better legendaries and restore a saved game.
https://gtm.steamproxy.vip/id/DripleD/myworkshopfiles/?section=guides&appid=449960

---

Terminator
Finish a big Freeplay game on Massacre difficulty without any form of healing
Doing this on nightmare will also unlock the two other achievments.

I recommend to do this on casual and with rogue and in maze or catacombs.
Be sure to unqeuip every card that gives healing, also be careful with the legendary divine potion Ambrosia.

Do this very slowly. Rogue has the greatest range of all and you can kill enemies from far away. In catacomb levels you can greatly utilize this as well.
The Invisible card(the legendary lets you use other cards), divine potions and especially the decoy spell let's you deal damage without beeing in any danger.

With Cheats:
Backup and restore a previous save after death.
You can use Cheat Engine to lock your health.


Hardcore nudist
Finish a medium or longer Freeplay game on Massacre difficulty without equipping any [additional] card
Only work with the random cards you are given. You can change their locations and variants.
You are allowed to die.

Like for Terminator I recommend casual and rogue because of her great range. Look at the cards you've gotten and decide if you want to try it or try again later.

With Cheats:
Backup and restore a previous save after death.
You can use Cheat Engine to lock your health.


Terrifying
Scare 75* monsters with a single Fear card use (Rogue only) *formerly 100

There are certain strategies, for example use a summoning monster near a door to spwan >75 monsters.
I found this very easily with Antipope on nightmare difficulty (in roguelike he spawn even more monsters).
Use a defensive build, HP regerneration, damage reduction and no AOE damage, focus only on the Antipope and use doors until he mass summons his 2nd or 3rd wave.
Use scare level 3, maybe also the Fan and walk around you should get this achievment pretty easily.

The Fastest & the Furiest
Defeat 200 monsters in 10 seconds

I recommend doing this with rogue. You can use the Antipope like I descriped in Terrifying. Use Decoy, Arrowrain, Flaming Leap+the other supportive cards you should be able to clear the whole room in less that 10 seconds. One legendary arrow type should also help a lot.

---

I supprisingly got this achievment in a normal hell level. With legendary arrows*, Armageddon (legendary Arrow Rain which deals even greater area damage), Flaming Leap, Intuition+Disenchant (legendary) and decoy.
Again see my other guide how to get better legendaries.

Rouge's massive range and great AOE, hells open space, disenchant+intuation (makes all enemies open to all types of damage) lets you clear a level from far away in extreme speed.

*I achieved this with poison arrows and shockwaves. Rogues double damage and double speed up from ring on poison deals more damage to more enemies over 10 seconds than the other elements.


I'm Invincible!
Resurect yourself 10 8 times in Rogulike mode playing one character

Beware in Freeplay you loose additional gold.

Despite the description I think this value is shared for different characters. I had one with 2 revives and the other unlocked this achievment on the 8th revive.
So you can just recreate roguelike characters and die&revive them at the early stage of the game with low costs.

Seams like this was lowered to 8 times, as it needs > 2 Million gold for just 8 times.

Grind grind grind, play it save, die at save locations by few enemies.
or...

With Cheats:
Increase your gold with Cheat Engine

Epic Armory, Unbelivable Library, Legendary Stash
Upgrade all [...] Cards to level 3

Sadly this relates to ALL cards and not just the class specific ones and involes a lot of grinding gold and runes.
Upgrade only the normal NON magical variants, these are way cheaper.

These are the only achievments where I really would recommend cheating as it takes a ton of time.

With Cheats:
Increase your gold & runes with Cheat Engine

Always ahead

Finish 5 dungeon levels without backtracing your steps

Find the stairs at the end of the level and leave without going back a step.
This can be done everywhere but some hell levels are linear if you want some direction.
After you have finished a level you can go back to loot it.