The monsters in Ultraman grew from small to big, and mutated into monsters because of changes in the environment. That series of Otto

There were many monsters in the Ultraman series that varied in size from small to large. These monsters usually mutated due to changes in their environment and evolved into stronger creatures. For example, in "The Ultraman Saga," a monster called "King Reid" was originally an ordinary frog. However, due to the changes in the underwater environment, it mutated and evolved into a powerful monster. Similarly, in "The Legend of the Galaxy," a monster called "the Giant Horn Beast" was originally an ordinary cow. However, due to the changes in the environment of the planet it was in, it mutated and evolved into a powerful monster. Therefore, the change in the size of the monsters in the Ultraman series was also due to the change in the environment they were in, thus evolving.