It is estimated that the Timurid army counted 140,000, mostly cavalry, and also 32 war elephants. Bayezid's army numbered 85,000. Historical sources exaggerated the number of troops; Ahmad ibn Arabshah claimed 800,000 Timurid troops, while a German witness claimed 1,6 million, for instance. The Ottoman force included contingents under his sons, Ghazis, Janissaries, Anatolian Muslim vassals, and various European  vassals. Among Serbian vassals participating were Stefan Lazarević and Đurađ Branković, and among Albanian were Koja Zakarija, Demetrius Jonima, Gjon Kastrioti, and probably Tanush Major Dukagjin. Christian vassals that did not participate is  Zetan Konstantin Balšić. A quarter of the Ottoman troops were recently conquered Tatars.
Question: How many Serbian Vassals participated?
Answer: 2