Here is the full list of all 11 Happy Game achievements. It takes around 1-2 hours to unlock all of the achievements on Windows.
Congratulations, you've endured the first nightmare. On to the next one!
You've found the book of the dead.
You've just seen a lot.
How many heads does it have?!
Knives are for cutting, not for licking.
You just make the hearts pop.
Delicious!
You've passed the second nightmare. You're almost happy now.
You've been... thunderstruck!
You've built a beautiful cairn.
Finally, it's over.