Young magician with the ultimate in spooky craft (7)
I believe the answer is:
pottery
'craft' is the definition.
(type of craft)
'young magician with the ultimate in spooky' is the wordplay.
'young magician' becomes 'Potter' (Harry Potter).
'with' says to put letters next to each other.
'the ultimate in' says to take the final letters.
The final letter of 'spooky' is 'y'.
'potter'+'y'='POTTERY'
(Other definitions for pottery that I've seen before include "baked goods" , "Ceramic ware" , "Clayware" , "Goods of fired clay" , "Items made from clay" .)