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