I have seen a lvl 16 whose challenges is zero!!!

Answer 1

Do you mean Pie Skill in @Hatsy Rei ?
She complete them all. 100%
So if you see her 0 skill tab, that because she remove it and not because she never do challenge.

If not, Who?

Answer 2

who ?

Answer 3

wow lol XD

Answer 4

I'm also interested to discover who ^^

... because reaching level 16 without challenging seems really difficult: only imaginable since few times ( best answer feature ), with much time spend on Q&A :P

Answer 5

Give that man a medal

Answer 6

Level is not only for making challenges, or even Learning. If you post a question or an answer with a lot of upvotes, you will unlock some badges, and rise levels. Is a social thing. 😉

Answer 7

lvl 16 only achievable without challenges. otherwise you end up lvl 1 again with only few losses 😅