This section discusses acheivements and the easiest way to acheive them.
Among the acheivements that are known include dieing in various forms, and winning in various forms.

There is an acheivement for not grabbing the Lantern from the Tavern and winning. As there are many hats that generate light in the game, and several weapons, and a single potion which makes the player generate more and more light which each one used, you should consider that as soon as you have mastered the basics of the game and surviving down to at least floor 5 a few times that you will no longer need to grab the Lantern at all for any of your runs. This will make you acquire this acheivement much much faster.

The acheivements for winning a certain number of time, as well as with the type of run... simply play, win, and start over... rinse and repeat until you win 10 times. Try the other modes afterwards...

There are also multiplayer acheivements. The only one that can be seen is the win in co-op.

There are acheivements for dieing... you can die of alchohol poisoning. To do this acheivement, easiest, grab all the beer from the Tavern. Play through the game never healing, and when you get to 9 or less health drink all the beer from the Tavern. There is 9 beers total. That will do 9 poison damage, killing you if you have 9 health or less.

You can also get an acheivement for dieing by falling in lava. This is a secret acheivement. Simply find lava and drop in. Lava traps are found typically after the first two floors.

Lastly, there are achveiments associated with Bosses. There are 13 bosses, and you can find all 13 without exploring every floor... there are also multiple versions of each boss, slightly different color and completely different names. Kill all 13 throughout all your runs to get an acheivement.
The hard version is killing all of them in 1 game run... meaning no dieing! This is hard, considering whether or not hard versions or normal versions are what is available depends on whether the boss appears on early floors or later floors/

As of yet I do not know of all unlockable classes/characters and have only discovered a few.

Also, some characters found in the dungeon become temporary companions and allies.

While exploring the dungeon you can find various friendly NPCs. If you locate them, you will have to decide on what to do to make them want to leave the dungeon with you.

The Dinoman Bruiser can be acquired by finding him in the dungeon and paying him 1000 gold to join you... however he will only be available for the one run you are on, and is thus temporary. He is absurdly powerful and has absurdly high health, and can solo multiple bosses all at once for you and come out alive.

Chickens can be found and pet, they will follow you. They level up by eating coins, and heal by eating coins, and they will also poop the coins they eat, so you can recover coins they ate by waiting for a battle to end and 'tapping' them. Chickens have low health and low damage, but their ability to level up and heal with coins makes up for it. They are temporary companions.

Wolves can be found, but they will attack you if you do not wear a Wolf Mask. If you wear a Wolf Mask, pet a Wolf and it will become friendly, following and attacking your enemies. Wolves have decent health and high damage. They are temporary.

Bears can be found, but they will attack you if you do not wear a Koala Bear Mask. If you wear a Koala Bear Mask and pet a Bear it will become friendly, following and attacking your enemies. They have high health and damage, like the Dinoman Bruiser. Also temporary.

The Knight can be found, and if found, can be high-fived to become a companion. If you take the Knight to the Tavern it becomes a permanent unlocked companion.

The Doctor can be found, and if found, requires a small puzzle to get him unlocked. I can't get him to follow me if I high five him, but the Remote Control apparently can teleport his Tardis around... I think its key to unlocking him.

The sister of Terry the Tip Dwarf can be found in the dungeon. I was told that if you find her and give her something she'll aid you, either apples or beer... can't remember well... she's called Perry.

There is supposed to be a Rogue, Cowboy, and Warlock... I do not know their names and how to unlock them...

The Nekomancer is a secret character that will join you as well. Simply locate him/her and his/her cats. The Nekomancer is located at a secret area that can only be entered by finding and using a remote control on the bottom floor 26 which unlocks the path to him/her.

I'll add more characters later... if there is anything more I find...