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.
You've built a beautiful cairn.
You just make the hearts pop.
Delicious!
How many heads does it have?!
You've just seen a lot.
You've been... thunderstruck!
You've found the book of the dead.
Finally, it's over.
You've passed the second nightmare. You're almost happy now.
Knives are for cutting, not for licking.
Congratulations, you've endured the first nightmare. On to the next one!