Hey Dushyant,

 you‘ll write the exam with your juniors and the level of question is same as that of the original board. In fact, the question paper for the regular candidate is same as that of the improvement candidate.

You will get a new mark sheet by CBSE.

If you score less in your improvement exam, then your previous marks will be considered. In short, only the best counts.

you will be able to apply for entrance exams but for that you need to sit for all the five subjects otherwise you will not be allowed to give the entrance exam.