 Hydraigen will be one of the best Pokemon to terastalize in Pokemon Scholar and Violet. Not only can Hydraigen get rid of one of its biggest type weaknesses in Fairy, by terastalizing into a Steel type it can gain even more benefit from its ability levitate. Meaning that Steel type ground weakness is not even an issue, only leaving it to worry about fighting and fire attacks. Making something like Gyarados with its flying and water type coverage an even better partner for it in competitive double battles. This is one of my top picks for terastalizing types and Pokemon going into Pokemon Scholar and Violet. Let me know yours.