There are 16 bosses, each 4 bosses per zone, starting from second.
2nd zone:3rd zone:
- Destroy the Torturers
- Destroy the Ogrim Brothers
- Destroy the Dremora Pirate
- Destroy Traveling Dremora
4th zone:
- Destroy the Daedroth of Kora-Dur
- Destroy the Ever-Open Eye
- Destroy the Daedroth General
- Destroy the Devourer of Souls
5th zone:
- Destroy the Frost Lord
- Destroy the Storm Lord
- Destroy the Xivilai Slavemasters
- Destroy the Seductive Sisters
- Destroy the Verkarth Vampire
- Destroy the Crescent Dremora
- Destroy the Lich of Mournhold
- Destroy the Son of Molag Bal
That's odd, because me and my friend fought two of his generals last-night in Cyrodiil. The Titan and some long named Daedroth General.