I think it would be fun to have students, when they reach a certain level to have a "final exam"! The professors of the school they have been trained in duels the student for a rare treasure card, or "last spell", the professor themselves, perform a devastating effect to the enemies!
When the student then completes the Malestaire and Celestia quests, have the final reward be a Malestaire, Celestia final boss treasure card or "last spell" to be added to their decks!
I think this would make the game come together nicely!
It's a good idea but it's too soon for a "final" spell. The game still has another 4 worlds to go even after Celestia is released. This could be a good idea for our level 98th spell though