Unclear what you're asking means just that: it is unclear what you are asking for in your challenge spec. In almost all cases, further details should be left by the close voters as comments.
While bonuses are discouraged, they don't make a challenge unclear, unless the specification of the bonus criteria itself is unclear. A do X without Y challenge doesn't have to be unclear, but it's very difficult to specify them properly. Unlike downvotes, close votes (if successful) aren't anonymous anyway, so there's no reason to not comment on the challenge.
Please note that using any of the things to avoid when writing challenges doesn't make a challenge off topic. These are mere guidelines which can (and oftentimes will) earn the OP a few downvotes, but unless it actually breaks an established rule, a challenge shouldn't be closed for ignoring them.
Finally, the close reasons are (mostly) the same on all Stack Exchange sites; the only thing we can customize are the off topic reasons. Since a challenge that is merely unclear is not off topic, that doesn't help us here.