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.
Once upon a time, there was a boy named Tom. One day, he found an old amulet in the attic. As soon as he touched it, he got hypnotic powers. He could make people do simple things like dancing or singing just by looking into their eyes. At first, he used it for fun at school, making his classmates do funny moves. But then he realized it could be misused, so he decided to keep it a secret and only use it for good, like helping a shy friend become more confident by hypnotizing him to believe in himself.
The story could start with the boy being an ordinary kid. One day, he comes across an old, strange object. When he touches it, he gets hypnotic powers. He then decides to use these powers to help his community. He might hypnotize people into cleaning up the neighborhood or being more friendly to each other.
It could be another person who also has some sort of mind - controlling abilities and wants to use the boy's powers for their own evil plans. This antagonist might try to trick the boy into using his powers in the wrong way.
Well, he might become even more powerful and be able to transform into new and amazing creatures. Maybe he could gain the ability to fly in his animal forms, which would be really cool.
One idea could be a story about a young wrestler's journey to overcome his fears and insecurities in the ring. He could have a mentor who helps him train and build his confidence, and the focus could be on his growth as an athlete.
Perhaps he gets a power related to mind control. This would allow him to influence the actions of his enemies or even make them fight among themselves. He could also gain a power that lets him absorb the powers of his defeated foes. So, every time he defeats an enemy, he becomes stronger by adding their powers to his own arsenal.
Obviously, Dipper is the main character as the title implies. His sister Mabel is often included too. She might react in various ways to Dipper getting powers, like being excited or a bit jealous. Wendy is also a common character. She could be a source of support or a love interest for Dipper in some fanfictions.
In this fanfiction, Robin might get powers as a result of a genetic mutation triggered by a rare chemical. These powers could include enhanced speed and the ability to see in the dark. He initially hides his powers from the team because he's afraid of how they'll react. But when a dangerous situation arises where his powers could be the key to victory, he reveals them and they all work together to defeat the enemy and accept his new status.