If you have a library card from a major city (e.g., Berlin, New York, London), check their e-lending platform. Many libraries stock the PONS 600 as an e-book that you can "borrow" for 21 days as a PDF.
It is designed to take learners from level up to B2 (Intermediate) . It covers the "big three" of German grammar struggles: pons 600 ubungen deutsch als fremdsprache pdf
Having the PDF is only 50% of the battle. Here is a 4-week study plan to effectively complete the 600 exercises. If you have a library card from a major city (e