Complete a quest

Easy one, just play the game and you will get it.

Beat a Boss

Easy one, just play the game and you will get it.

Unlock a door

Easy one, just play the game and you will get it.

Unlock Chest

Easy one, just play the game and you will get it.

Beat Game with Assassin
Beat Game with Warrior
Beat Game with Shaman
Beat Game with Wizard

Easy ones, the quickest way to get them is to beat the game in "Easy" mode with each class. I have done this for the Warrior, the Wizard and the Shaman. I used the Assassin to get the higher difficulties achievements.

Remember to be careful with your life, clean the entires floors to get the most of them (xp, money and items) and USE YOUR SKILLS !

Pick 1M Gold

Easy one, just play the game and you will get it after beating the game 3 or 4 times. You do not have to gather 1 million gold in one game, it accumulates through your different games !

Buy all stock

Easy one, just buy all you can from one specific merchant (only one floor, no matter which one). Do it before selling your items, otherwise you will have to buy them back because they are going to be available in the shop !

Find 50 hidden stash

Easy one, just play the game and you will get it.

You listened until the end

Easy one, you have to listen until the end after defeating the final boss. Just do not skip the final scene, you have to wait.

Complete 50 quests

Easy one, just play the game and you will get it.

Beat Game in Easy
Beat Game in Normal
Beat Game in Hard
Beat Game in Hell

Beating the game in Hell will only unlock the "Is this Hell?" achievement. You have to beat the game in Easy, Normal and Hard to unlock all of them. I am going to explain how to unlock the Hell one. For the three remaining ones, just use this explanation knowing that it will be easier.

Firstly, I used the Assassin to do it. Being able to use ranged attacks without mana requirements is too powerful to be overlooked.

Then, with the Assassin, you will not regen your life by walking (I do not know if it is the same for the other classes, I guess so) in Hell mode (even in Hard mode). That is why you have to be very careful, take all the food you can in order to be able to get your life back when you can. Useful hint : you will get your full life back after levelling up, so do not use food/potion if you are about to level up !

Being careful means that you have to walk slowly and check everything around you after each step. It can be quite frustrating, but going quickly through a room will often leads to your death or at least it will empty your food/potion stock. It applies to rooms that you have already walked through because monsters can spawn at everytime.

You should get the most of each floor : kill all the monsters and get every loot to gather money and stuff. Complete the quests but only after cleaning the entire floor. This way, you will be able to fight bosses from quests without worrying about regular monsters. Trigger traps, you will find more monsters.

Regarding the bosses, you have to use these tricks :
- use warp portals;
- use your skill "Sleep" (Good Night).
This is how it works : when you see a boss, use your regular attacks or your skills until the boss arrives in front of you. Then, you should take no risk and escape until you find a warp portal. Use this portal (cleaning the entire floor before means that you should be safe on the destination side) and go back to the boss, you will be able to throw some more arrows. Do this until the death of the boss. Do not take any risks, your attacks/skills may be dodged and critical hits from bosses can kill you out of nowhere !
Once you get the "Sleep" skill, you do not need the warp portals, just use the skill (it cannot fail !), get back, throw some arrows (the first hit will awake the boss) and as soon as the boss is in front of you, walk around until the end of the cooldown, use "Sleep" again, ... and the boss will eventually die.
IMPORTANT : If you encounter a boss that can perform ranged attacks, you should just run (close the door you have just opened, use "Sleep" and do not look back, use warp portals or stairs, ...) ! The two tricks do not work against these bosses. You could kill them, but you will have to spend too much health (food/potion).

Buy every red potions you can. You might need them if you get unlucky, especially against regular monsters that have ranged attacks that can burn/freeze/bleed/...
Buy also the keys : being able to open both doors and chests will be quite rewarding.

Finally, the final boss !
Sadly, you will need a bit of luck to defeat him ... I mean, if his "Death" skill hits you, you will likely die, except if you can kill him, get the skull key, open the chest and get the lamp within ten turns !
Be careful with the scythe, a melee attack can deal a lot of damage. But, if you have a good stuff and a good level (you should be level 13-15), it should be okay because you will most likely be able to kill him before he gets near you. Watch out for your life, and think about a critical hit : if it can kill you, just use a red potion. And, to conclude, remember that killing the final boss does not mean that it is over : you have to open the chest, and you might find some monsters on your way ... once again and for the last time, be careful !

Beat Game in 30m

I did it using the Assassin in "Easy" mode.

Since you are getting your life back by walking, do not hesitate to rush through the rooms, you will save time and it is not that bad to get hurt by monsters.

You should not clean the entire floors (quests, bosses, monsters, ...) : as soon as you feel that your stuff allows you to handle the next level, use the stairs to go down !

You should use a watch to check time, and it should be fine !

Defeat 20 Bosses

Easy one, just play the game and you will get it.

Disarm a trap and get loot!

Easy one, you have to play the Assassin, be near a trap, click on it (not walk on it) and hope that it will get disarmed and not triggered.

Beat Rackan Mansion

Easy one, choose the adequate mode and just stick to the plan described for other achievements in order to unlock it.

Defeat 3 ghosts of a past Hero

Easy one, especially if you suicide your hero at level 1 / first floor, then kill your ghost quickly with a new hero.

Beat a Custom game in Hard or above with 10 floors

Choose the Assassin, Custom Game, Hard and the biggest dimension available : it enables you to have access to more monsters so more xp (and maybe more quests ? Not sure about it).

Then use the tips I give to beat the game in Hell, and you should be fine. Being careful and killing everything allowed me to reach the final boss at level 25, so I was able to one-shot it with "Bullseye".

Beat Game with NecroDancer

Choose the "Easy" difficulty and use the tips I give above to reach the final boss with the highest level possible.

Then, the way I defeated it was using the skill "Summon" so that my minion could take the aggro while I used "Fireball" on him, trying to trigger "Combustion" to kill it quickly (because regular damage ... meh).

You may need some mana potions, and if you feel in danger, do not hesitate to use the "Teleport" skill to escape. You'd better come back with all of your skills available to be cast and full mana rather than die right before getting this achievement !

Beat the Rothar Mansion

New content has been added, but you just need to complete the new map on Easy to unlock this achievement. So I suggest you use the tips I gave above to beat Hell with the Assassin, and you should be fine !