The Orc Priest Augustus that was supported by Yang Ling, started changing the number and the species of Magical Beasts repeatedly. Even though they failed repeatedly and didn't get good mutant Magical Beasts, they still started grasping and understanding some patterns and rules.
If they refined Evil Eyes and spiders together, they would either get a stupid ugly monster or nothing. If they refined Vampire Bats and horned beasts together, they would get a Magical Beast slower than Vampire Bats that didn't have the horned beasts' venomous strings.
However, if they refined two low-level Magical Beasts such as Vampire Bats and spiders together, they would get an appropriate Magical Beast that retained the spiders' venom attack, sneak-attack gifts as well as a pair of bats' wings. It could fly at a low-altitude like flying spiders.