Articles are complicated, but the main idea is usually: We use 'the' if there is one thing (or group of things) and the *listener* knows which one you are talking about. So, with that in mind... 1. Most likely 'the mirror', because most people think of the main mirror in a person's home. Other examples of 'main things' are: the lake (our community has one main local lake), the pub (traditionally there was one per town or neighbourhood), the post office (same). 2. Most likely 'the contract'. There is probably only one and the listener knows which one you are talking about: his! 3. Both are correct! 'No matter your level' (a known phrase). 'No matter what your level is' (a normal sentence). Phrases don't always make sense, because they use older or less common English. I hope that helps :)

I agree with Loki that articles can be complicated. In my opinion, MIRROR doesn't follow the usual rules: People frequently say, "Look in the mirror," meaning something like "look in ANY mirror." But saying "look in A mirror" would not be wrong.