Has anyone completed every achievement? I just want to see what a completed list looks like.

I don't know, but the hardest achievement is "Win 10,000 games." There are only a handful of people who have achieved this, so I'd start by looking at them.

Would it be possible for you to give us a list of all the achievements? How many challenges are there altogether?

Another thing, it would be good if you could somewhere note down the number of challenges completed by an individual player on their page.