Complex sentence: John discovers his third legacy, the ability to communicate with animals and also finds out that bernie kosar is a chimaera, and convinces one of the Mogadorians' beasts to turn on its masters.
Split into simpler sentences: John discovers his third legacy, the ability to communicate with animals. He realizes that (his supposed pet dog) Bernie Kosar is a "chimaera" (a shapeshifting creature), and he convinces one of the Mogadorians' beasts to turn on its masters.