and you will find this statement: "You have a high chance of getting an offspring of your current pet and you have a small chance of getting a rare hybrid of the two pets."
Conversely, Level 58 school pets, when hatched with each other give a hybrid egg 100% of the time.
yeah, i have often been unlucky in my hydra hatches but luckily, i got the helion (fire hydra) and leviathan (storm hydra) someone told it was a 50% chance of getting a hybrid