Complex sentence: It was taken by Nerissa who tricked Elyon into accepting a jewel from her mother's crown, which absorbed her magic and, after it was fully absorbed, tricked Elyon again into making her willingly give it up, taking her powers in the process.
Split into simpler sentences: It was taken by Nerissa, who tricked Elyon into accepting a jewel from her mother's crown, which absorbed her magic. Elyon was then tricked into willingly giving it up, taking her powers in the process.