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