Cryptic shone fantastically: a spectacular display! (12)
I believe the answer is:
pyrotechnics
'a spectacular display' is the definition.
(firework display)
'cryptic shone fantastically' is the wordplay.
'fantastically' indicates an anagram.
'cryptic'+'shone'='crypticshone'
'crypticshone' anagrammed gives 'PYROTECHNICS'.
(Other definitions for pyrotechnics that I've seen before include "Fireworks" , "Firework display" , "sparkling display" .)