Little Mong's Big Secret

The most unusual and, perhaps, harmless creatures in the underwater world are little mongs. However, this is only at first glance.
 
When the mongs are still small, they often come to the surface and make contact with the inhabitants of coastal villages. But when they grow up, they turn into huge voracious monsters that hunt underwater inhabitants. It is said that an adult mong is even able to destroy the azure deep.
 
It is noteworthy that all these stories come from a village whose inhabitant saw the underwater sword of Scaurus. Therefore, the magicians of Ericuria do not believe in it. However, they studied small Mongs and came to the conclusion that they could not grow in size.
 
However, not a single expedition was sent to the deepest depressions in the ocean. Are the magicians really hiding something from the inhabitants of the kingdom?