Chapter 12 mainly deals with the

1. Marriage of Vasudeva
2. Children of Vasudeva
3. Birth of Kauravas and Pandavas
4. Avatar of Sri Bheemasena
5. Avatar of Lord Sri Krishna
6. Death of the devil Poothana
7. Death of the devil Shakatasura
8. Birth of Arjuna
9. Death of the devil Trinavarta
10. Birth of the two sons of Madri namely Nakula and Sahadeva

Chapter 13 mainly deals with

1. Various miracles and extraordinary feats demonstrated by Lord Sri Krishna
2. respectful hospitality by the wives of the Brahmins to Lord Krishna
3. Govardhana Giridhari Lord Sir Krishna
4. Divine sport with Gopikas
5. Slaying of Arishtasura and others by Lord Krishna
6. Journey to Mathura
7. Akrura’s fortune in having splendid dharshan of Lord Krishna in the waters of Yamuna River
8. Extraordinary activities in Mathura by Lord Krishna
9. Killing of Kamsa

Sloka 12 and 13 of Bhaava sangraha is also explained.