"Assimilating New Creatures" 

The animal transformer domain master actually had a strong domain with so many strange creatures inside his domain, but that only worked when the enemy's domain was weaker or equal to his domain, so that the creatures inside his domain could enter the enemy's domain. 

After all, when a domain was weaker than another domain, it would be 'swallowed', which means the two domains overlapped. 

When the domain was equal, it would still have a certain intersection where creatures from both domains could enter the other domain through this intersection. 

It would be even better if the enemies entered the domain full of strange creatures. 

The domain master himself could also turn into various strange creatures to strengthen himself, which was why he was nicknamed the transformer.