1) I don't know if yours is technically incorrect, (except for "it it", which i assume is a typo) but certainly "It never works when you need it to" would be much more common. 2) okay except for capitalization 3) (based on

I used part tense in 1 and 2 to show that the speaker''s ownership came before the other person's claim.

1. He/she was my dog before he/she was yours! 2. This was my house before it wa yours. I own it! 3. As of now/from now on .... 4. fine

These are not complete sentences. They all need a subject -- what is sending shooting pains through your back?

An atheist believes that there is no God. An agnostic believes that we have no way of knowing for sure if there is a God or not.

"Nothing much" is not a common or logical reply to "How are you doing." How are you doing? Fine/Okay/Not bad/So-so What's new?/What's up?/What's happening? Nothing much.

3 -- Jane Austen uses "gentleman-like," but I don't think anyone uses it in this century. And your sentence #3 doesn't make sense -- if he's always a gentleman, then of course he's a gentleman whether he wins or loses.

It's a very strange phrase. Where did you hear or read it? What was the context?

Yes, that's how I would understand it.

Do you mean a crowd? Please try to actually ask a question in your post instead of just writing a phrase.