Their powers could also interact in a more subtle way. Say, Beast Boy turns into a small animal to hide from danger, and Storm creates a thick fog with her powers to further conceal him. This would show how they can use their powers in tandem for protection.
Storm's weather - controlling powers and Beast Boy's shape - shifting could interact in a combat scenario. For example, Beast Boy could shift into a large bird and fly into a storm cloud created by Storm to gain an aerial advantage against an enemy.
Storm's power over the weather could be enhanced by Beast Boy's animal forms. For example, if Beast Boy turns into an eagle and flies into a storm cloud that Storm has created, he could disrupt the electrical charges in a way that Storm can then manipulate to create a more powerful lightning strike.
Beast Boy's power to transform into animals could be affected by Storm's weather control. For example, if Storm creates a strong wind, it could either help Beast Boy fly faster in his bird form or make it difficult for him to stay in the air if he's not used to such strong winds. Also, if Beast Boy turns into a cold - climate animal like a polar bear, Storm could make the area around him even colder, enhancing his natural abilities in that form.
Beast Boy's power to transform into animals could complement Storm's weather - controlling abilities in many ways. For example, if they are in a battle and Storm creates a powerful windstorm, Beast Boy could transform into a bird and ride the winds to gain a strategic advantage. Or if they are in a desert environment, Beast Boy could turn into a camel while Storm creates a rain cloud to bring water.
Their powers could interact in really cool ways. Zatanna's magic could be used to enhance Beast Boy's shape - shifting. For instance, she could use a spell to make his animal forms stronger or faster. In return, Beast Boy could use his animal senses when they're on a mission together. If Zatanna is trying to find a hidden magical item, Beast Boy in his animal form could sniff it out or sense it in a way that Zatanna's magic alone might not be able to do.
One possible fanfiction could involve Beast Boy and Storm meeting in a multiverse scenario. Maybe Beast Boy is on a mission in Storm's world and they initially clash due to their different powers and personalities. But as the story progresses, they start to understand and respect each other's abilities and end up working together to defeat a common enemy.
Beast Boy could use his powers to his advantage in the environment of Star Labs. He might transform into a small creature to sneak into restricted areas to find out what the scientists are up to. Or he could turn into a large and strong beast to protect the lab from outside threats that the normal security systems can't handle.
A Beast Boy x Storm fanfiction could center around a crossover adventure. They could be brought together by a powerful magical artifact that has the potential to destroy both of their worlds if not stopped. Their combined powers would be interesting to write about, with Beast Boy's agility and animal forms complementing Storm's control over the weather.
It could be an ancient and powerful wizard. Maybe the wizard sees potential in Beast Boy and decides to grant him new powers to help him in his fight against evil.
Beast Boy's power might be affected in that he could have trouble shifting shapes. When sick, his body may not be able to handle the energy required for complex transformations. For example, he tries to turn into an elephant but can only manage a small mouse form.
One idea could be that Beast Boy and Storm meet during a strange weather phenomenon caused by a new super - villain. Beast Boy, being able to transform into various animals, could use his abilities to help Storm, who controls the weather, to combat the villain. For example, he could turn into a flying creature to help her reach the source of the abnormal weather in the sky.