Here is the full list of all 42 Knights of Pen and Paper +1 achievements. It takes around 20-25 hours to unlock all of the achievements on Windows.
Use a potion while full health.
Unlock the Game Developers that made the game.
Unlock the Bard class.
Clear a dungeon.
Reach Level 15 in a specific Spell.
Unlock the Barbarian class.
Reach Level 15 in any character.
Unlock the Hunter class.
Gather 10 grindstones from veins.
Make the blacksmith dance.
Roll 20 in any random roll.
Gather a grindstone by mining veins.
Win a battle with 7 monsters.
Kill an elite minion.
Reach Level 5 in any character.
Roll 1 in any random roll.
Unlock the Knight class.
Unlock the Necromancer class.
Unlock the Shaman class.
Kill a dragon.
We know it may be frustrating to die so we've just rewarded you with this achievement. Do not give up, the game is about to begin!
Continue the game after a game over.
Complete a campaign using all 5 Game Developers as characters.
Play with all classes in game.
Play with all characters in game.
Visit your Kitchen inside the game.
Spend 9.001 golds.
Earn 9.001 golds.
Buy the highest weapon upgrade available.
Buy the highest armor upgrade available.
Reach Level 30 in any character.
Reach Level 30 in a trio.
Reach Level 30 in every character of your group.
Finished the campaign.
Choose a weird combination of character and class.
Unlock a new master.
Unlock all masters.
Finish the storyline as fast as you can (less than 365 days but you may extend that to 465).
Visit every single place in game.
Buy all goodies in game.
Clear 10 dungeons.
Clear 50 dungeons.